Process Plant / Utility Area
Piping layouts, Site plan and Plot plan
: Consideration of plot plan layout is related to an Oil Refinery or Chemical Plant. However, the majority of Process Plants require a plot plan with somewhat less stringent and less complicated arrangements. Equipment spacing requirements will vary with the type of plant and location. It is the responsibility of piping engineer. The best placement of equipment, leads to good piping layout. Plot plans are considered key documents to projects and are normally initiated in the pre-contract, conceptual and development stages of a proposal. After the contract is awarded for engineering, plot plans are developed at a rather rapid pace with very limited information. This early stage plot plan usually is very limited in detail, containing only enough dimensional data to define the outer limits of the available property selected for plant development. Located within the boundaries of the available property, rough equipment sizes and shapes are pictorially positioned, along with anticipated pipe rack configurations, structure shape and rough sizes. The plot plan at this level of detail is then used for construction evaluation and is normally submitted to the client for approval.
- Plot Plans and Equipment Layout: Arrange equipment, structures, and piping to permit maintenance and service by means of mobile equipment. Provide permanent facilities where maintenance by mobile equipment is not practical. Group offsite equipment, pumps, and exchangers to permit economical pipe routing. Locate this equipment outside of dike wall storage areas. Space for future equipment, pipe, or units should not be provided unless required by the client or for specific process considerations. When applicable this requirement should be indicated on the plot plan and P & I Ds.
- Process Piping: Locate all pipe lines in major process units on overhead pipe ways. In certain instances, pipes may be buried, providing they are adequately protected. Lines that must be run below grade, and must be periodically inspected or replaced, should be identified on the P & I D and placed in covered concrete trenches. Cooling water lines normally may be run above or below ground, based on economics. Domestic or potable water and fire water lines should be run underground.
- Gap between pipes: With full consideration of thermal movements, clearance between the outside diameter of flange and the outside diameter of pipe to the insulation should not be less than 1 inch or 25 millimeters. Clearance between the outside diameter of pipe, flange, or insulation and any structural member should not be less than 2 inches or 50 millimeters.
- Orifice Runs and Flanges: Locate orifice runs in the horizontal. Vertical orifice runs may only be used with the approval of company control systems engineering. Orifice flanges with a centerline elevation over 15 feet or 4.5 meters above the high point of finished surface, except in pipe ways, should be accessible from a platform or permanent ladder. Location of orifice taps for air and gas should be from top and preferably with vertical centerline, or 45 degrees above horizontal centerline. For Liquid and Steam, it should be with horizontal centerline or 45 degrees below horizontal centerline.
- Pressure Instruments: Locate all local pressure indicators so that they are visible from grade, permanent ladder, or platform. Those located less than 15 feet or 4.5 meters above high point of finished surface should be accessible from grade or a portable ladder. Those located in a pipe way should be considered accessible by portable ladder. Those over 15 feet or 4.5 meters above high point of finished surface should be accessible from a platform or permanent ladder.
- Temperature Instruments: Locate temperature test wells, temperature Indicators and thermocouples to be accessible from grade or a portable ladder. Those located in a pipe way should be considered accessible by a portable ladder. Those located over 15 feet or 5 meters above high point of finished surface should be accessible from a platform or permanent ladder. Locate all local temperature indicators in such a manner that it should be visible from grade, ladder, or platform.
- Sample Connections: Locate all sample connections so they are readily accessible from grade or platform. In general, where liquid samples are taken in a bottle, locate the sample outlet above a drain funnel to permit free running of the liquid before sampling. Hot samples should be provided with a cooler.
- Spectacle Blinds: Locate spectacle blinds to be accessible from grade or platform. Blinds located in a pipe way are considered accessible. Blinds that weigh over 100 pounds or 45 kilograms should be accessible by mobile equipment. Where this is not possible, provide davits or hitching points. Closely grouped flanges with blinds should be staggered.
- Steam Traps: Locate all steam traps at all pocketed low points and at dead ends of steam headers. Also, provide traps periodically on excessively long runs of steam piping, for sufficient condensate removal, and to ensure dry quality steam at destination. Steam traps should be accessible from grade or a platform. Steam traps located in pipe ways should be considered accessible by portable ladder.
- Utility Stations: Provide and locate utility stations with water, steam, or air in such a way that all areas should be reachable with a single 50 foot or 20 meters length of hose from the station. Provide water outlets at grade level only, in pump areas, and near equipment that should be water washed during maintenance. Provide steam outlets at grade level only in areas subject to product spills, and near equipment that requires steaming out during maintenance. Provide air outlets in areas where air-driven tools are used such as at exchangers, both ends of heaters, compressor area, top platform of reactors, and on columns at each man way. Hose, hose rack, and hose connections should be provided by the client or be purchased to match the clients existing hardware.
- Vents and Drains: The P & I D should indicate, locate and size all vents, drains, and bleeds required for process reasons and plant operation. Provide plugged hydrostatic vents and drains without valves at the high and low points of piping. Provide valved bleeds at control valve stations, level switches, level controllers, and gage glasses per job standard.
- Valve Operation: Locate operating valves requiring attention, observation, or adjustment during normal plant operation as noted on the P & I D, so they may be within easy reach from grade, platform, or permanent ladder. 2 inch or 50 millimeters and smaller may be located reachable from a ladder. 3 inch or 80 millimeters and larger must be reachable and operable on a platform. Operating valves with the bottom of hand wheel is over 7 feet or 2.1 meters above high point of finished surface or operating platform may be chain-operated. The centerline of hand wheel or handles on block valves used for shutdown only, located less than 15 feet or 4.5 meters above high point of finished surface, and those located in pipe ways, may be accessible by portable ladder. The centerline of hand wheel or handles on block valves used for shutdown only and located over 15 feet or 4.5 meters above high point of finished surface, except those located in pipe ways, should be operable from permanent ladder or platform. In general, keep valve hand wheels, handles, and stems out of operating aisles. Where this is not practical, elevate the valve to 6 feet 6 inches plus or minus 3 inches clear from high point of finished surface to bottom of hand wheel. Clearance between the outside of hand wheel and any obstruction should be 3 inches or 80 millimeters.
- Insulation Shoes and Cradles: Locate Insulation shoes anywhere a line crosses a support for hot insulated piping when the piping is 3 inch or 80 millimeters and larger, carbon and alloy steel lines with design temperatures over 650 degrees Fahrenheit or 350 degrees Celsius. Large diameter lines of 20 inches or 500 millimeters and over, stainless steel lines where galvanic corrosion may exist, lines with wall thickness less than standard weight, and vacuum lines should be analyzed to determine if shoes or wear plates are needed. Provide cradles at supports for insulated lines in cold service and for acoustical applications.
- Personnel Protection: Locate eye wash and emergency showers in all areas where operating personnel are subject to hazardous sprays or spills, such as acid. Personnel protection should be provided at lines that are not insulated, and for equipment operating above 140 degrees Fahrenheit or 60 degrees Celsius, when they constitute a hazard to the operators during the normal operating routine. Lines that are not frequently used, such as snuffing steam and relief valve discharges, may not require protective shields or coverings.
- Walkways: Walkways should have a 2 feet 6 inches or 1 meters horizontal clearance, which may not necessarily be in a straight line and headroom of 7 feet or 2.1 meters.
- Platforms: Minimum width for ladder to ladder travel should be 2 feet 6 inches or 800 millimeters. Headroom should be 7 feet or 2.1 meters and headroom from stairwell treads should be 7 feet or 2.1 meters. Minimum clearance around any obstruction on dead end platforms, should be 1 foot 6 inches or 500 millimeters.
- Ladders & Cages: Maximum height of a ladder without a cage should not exceed 15 feet or 4.5 meters. Maximum vertical distance between platforms should be 30 feet or 9 meters. Cages on ladders over 15 feet or 4.5 meters high shall start at 8 feet or 2.5 meters above grade. Minimum toe clearance behind a ladder should be 7 inches or 200 millimeters. Minimum handrail clearance should be 3 inches or 80 millimeters.
- Loading Racks: Locate loading and unloading facilities that handle flammable commodities a minimum of 200 feet or 60 meters away from process equipment, and 250 feet or 75 meters from tank area.
- Sleeper Pipe Supports: Normally, route piping in offsite areas on sleepers. Stagger the sleeper elevations to permit ease of crossing or change of direction at intersections. Flat turns may be used when entire sleeper way changes direction.
- Railroads: Headroom over through railroads from top rail should be 22 feet 6 inches or 7 meters. Clearance from track centerline to obstruction should be 10 feet or 3 meters. Verify conformance with local regulations.
- Safety Access: Provide a primary means of continuous and unobstructed way of exit travel from any point in any building, elevated equipment, or structure. A secondary means of escape should be provided where the travel distance from the furthest point on a platform to an exit exceeds 75 feet or 25 meters. Access to elevated platforms should be by permanent ladder. Safety cages should be provided on all ladders over 15 foot or 4.5 meters. The need for stairways should be determined by platform elevation, number of items requiring attention, observation and adjustment, and the frequency of items. Ladder safety devices such as cable reel safety belts and harnesses, may be investigated for use on boiler, flare stack, water tank, and chimney ladders over 20 feet or 6 meters in unbroken lengths in lieu of cage protection and landing platforms.
- Roads: Major process plants normally have three classes of roads. They might be called Primary roads, Secondary roads and Maintenance access ways. Normally secondary plant roads may be used as tube pull areas. Clearance or distance required.
|Road type||Vertical||Width||Shoulder||Side or off road|
|Primary||21'-0" (6.5m)||20'-0" (6m)||5'-0" (1.5m)||20'-0" (6m)|
|Secondary||12'-0" (3.7m)||12'-0" 3.7m)||3'-0" (1m)||10'-0" (3m)|
|Maintenance access||10'-0" (3m)||10'-0" (3m)||(not required)||5'-0" (1.5m)|
- Vertical Vessel Components: The pressure containment elements of the vessel are based of the process requirements for pressure, temperature, commodity, corrosion rate, plant life criteria, and the applicable Codes. The important components include the Shell, heads, and nozzles.
- Shell: The shell of the vertical tray vessel will have many variables. Wall thickness of the shell may vary. It may have different material at top verses bottom. It can be a single layer verses. multiple layer or cladding. Some parts of the vessel may have post weld heat treatment. It may have vacuum reinforcement rings and insulation support rings.
- Heads: Heads for vessels will have different shapes. The Dished head is a flatter version of the Semi-Elliptical head. The traditional torispherical head is used on process plant pressure vessels. The Spherical is sometimes referred to as a round head or Hemispherical-head. The top head and the bottom head may be the same shape but they will have some differences. It may have same material as that of Shell. It may be of thicker material for reinforcing or may be thinner material. Instead of dished end, there can be a conical bottom.
- Nozzles: Nozzles are pipes with flanges welded to it. It is used do put in or take off liquids or vapors and are placed at different locations, orientation and elevations. A piping engineers decides the location, orientation and elevation of each nozzle. Some nozzles are reinforced by a pad on shell. There are a number of nozzles on a reaction vessel or distillation tower.
- Overhead Vapor Outlet Nozzles: The overhead vapor outlet nozzles on a vertical vessel can have some latitude when it comes to attachment location. The attachment connection can be direct to the top head of the vessel or may be from the side. When the connection is from the side there will normally be a pipe inside the vessel angled up to the top head area. Small vapor outlet nozzles from small diameter vessels can be located out the side of the vessel and still be cost effective. Large diameter vapor outlet nozzles on large diameter vessels will be more cost effective if attached to the top head. The line is then looped over to the selected pipe drop position to go down the vessel.
- Feed Inlet Nozzles: All vertical fractionation vessels will have a feed inlet nozzle. This feed nozzle is special and critical on some vessels. Refinery Crude columns and Vacuum columns are examples that have this type of nozzle. This nozzle installation is characterized by the attached line originated at a fired heater, High temperature, High velocity, Mixed phase flow. It may require internals such as a distributor pipe or impingement plate. A Feed Transfer nozzle will normally be the key nozzle for any large fractionation vessel. Normally any side inlet orientation is possible but in most cases this will then dictate the tray orientation.
- Liquid (secondary) Inlet Nozzles: A normal liquid feed nozzle will not have the same complexities as the Feed Transfer type. This nozzle installation is characterized by the attached line originated at an exchanger, hot but not overly high on the temperature scale, some may have potential for mixed phase flow, normal line velocity. It may require vessel internals such as a distributor or inlet pipe. Watch Instrument connections should be in relationship to Inlets and reboiler returns.
- Reflux Nozzles: A normal reflux nozzle will not have the same complexities as other nozzles. This nozzle installation is characterized by the attached line originated at a pump, low on the temperature scale, all liquid flow, normal line velocity. It may require internals such as a distributor or inlet pipe. Multiple pass trays will require a more complex distributor or inlet pipe than a single pass.
- Draw-Off Nozzles: The purpose of this nozzle is to draw-off or remove the primary product. They are also used to Draw-off a secondary product to side stream stripper. May be installed with a sump to remove unwanted water in the process stream. This nozzle is located in the down-comer area of the column, it may be in a sump. It may be a larger size than the normal attached line size. Some of the initial vertical drop will be the larger size. It should be as per normal line velocity and may require internals if multiple pass trays.
- Bottom Reboiler Feed Nozzles: The liquid outlet nozzle will normally be in the center of the bottom vessel head. This nozzle is located in the bottom of the surge section of the column. It may be a very large size and has normally very low line velocity.
- Side Reboiler Feed Nozzles: This is also a potential Key Nozzle. The liquid outlet nozzle must be oriented in the same quadrant as the bottom down comer. This nozzle is located in the down comer area of the column and is in a sump. It may be of a larger size than the normal attached line size. Some of the initial vertical drop will be in the larger size. Normally liquid flow in line is at lower velocity. Relationship to elevation of associated reboiler is critical to nozzle elevation and internals.
- Side Reboiler Vapor Return Nozzles: One of the primary issues with this nozzle is the orientation relative to the other internal items and nozzles. If not placed in the right place the velocity of the return can blow liquid out of a seal pan or can affect the readings of any instruments attached to the far wall. This nozzle is attached to the line originated at a thermo-siphon or kettle type reboiler. It has a very high temperature, with moderately high velocity. All flow is vapor. It may require internals such as a pipe or impingement plate. Relationship to elevation of associated Reboiler is critical to nozzle elevation and internals.
- Bottoms Out and Drain Nozzles: The bottoms nozzle is normally a source for pump suction. The standard type is located in the bottom head then piped through the skirt with a drain nozzle off the bottom out line nozzle. This would be a combination nozzle. A variation of the bottoms nozzle is the siphon or winter type. This type may be used with the approval of process when bottom clearance is a problem. It is common industry practice to avoid locating any flanged connections inside the vessel support skirt. All flanges are subject to leaks, and vessel skirts are classified as a confined space.
- Level Instrument Nozzles: Extreme care must be used when locating level instrument nozzles. There are access and clearances problems that must be considered on the outside of the vessel. There are sensing location and turbulence problems associated with the inside of the vessel. These nozzles must be attached in the same pressure volume of the vessel. Lower nozzle should be in liquid of the surge section, and upper nozzle should be in vapor space. It should be located in static area or with stilling well. It requires external access for operation and maintenance.
- Pressure Instrument Nozzles: Pressure readings are normally taken in the vapor area of a vessel. Pressure connections shall be located in the top head area, 3 to 6 inches under a tray, or well above any liquid level in bottom section. These nozzle is generally located in a vapor space of the vessel. It requires external access for operation and maintenance.
- Temperature Instrument Nozzles: Temperature readings are normally taken in the liquid area of a vessel. Temperature connections shall be located 2 to 3 inches above the top surface of a tray, in the down comer, or well below any liquid level in bottom section. These nozzle should be located in liquid in the down comer area. It requires external access for operation and maintenance. It should not interfere with internals. Vapor temperature readings may be required for some situations. When required the preferred location is in the down comer area half way between the two trays. Tangential or Hillside connections may be required due to the thermowell length or to accommodate access from the ladder and platform arrangement. With the Process Engineer's approval investigate the possibility of raising or lowering the temperature point one tray for better ladder and platform arrangement.
- Steam-Out Nozzles: Process plant vessels that contain hydrocarbon or other volatile fluids or vapors will normally have a Steam Out Nozzle. This nozzle has a number of options. A simple blind flanged valve on the nozzle can be installed after the plant is shut down by Operations, the maintenance group would remove the blind flange from the valve. They then attach a temporary flange fitted with a hose coupling and proceed to steam out the vessel by connecting a hose from a utility station. A blind flanged valve and hard piped steam line configured with a steam block valve and a swing elbow can also be installed. A fully hard piped connection from a steam source can be provided. This method would have double block valves, a bleed, and a spec blind for positive shutoff. The vessel steam out nozzle should be located near the bottom surge section manhole on vertical vessels.
- Manholes: Manholes are also considered a nozzle. They just do not have any pipe attached to them. They are however, a very complex piece of the vessel orientation puzzle. The types of manholes normally relate to the method of cover handling provided. Manholes come in the following types. A Manhole may be hinged for side mount, for top mount, or for bottom mount. A Manhole may have davits for side mount or top mount only. A Plain Manhole may be for side mount, for top mount, or for bottom mount. The manhole orientation in top or non tray section of a vertical vessel is somewhat flexible. Normally any orientation is possible. However, the orientation of the manhole should be checked to insure that the entry path is not blocked by any internals. The Manhole may be located in the top head on large diameter vessels if there is a platform that is required for other items. Top Manholes on large diameter vessels have their built in good points and bad points. The good point is that during shutdown the open manhole provides for better venting. It also allows for a straight method for removal and reinstallation of the trays. The bad point is that ladder access must be provided down to the top tray, and the manhole is competing with the other nozzles for the space on the vessel head. Orientation for manholes that are located in the tray section of the vessel is more complicated. The location of between the tray manholes has a number of restrictions. These restrictions include the type of trays and the tray spacing. The first choice for the location of a manhole is between the down comers. The last choice is in the down comer space, but behind the down comer. The down comer would be fitted with a removable panel to allow further access into the vessel. The location to be avoided is above a down comer where there is the potential for falling down in the down comer space and injury. It would be better to seek approval to move the manhole up or down one tray than placement over a down comer.
Manhole orientation in the surge section of a vessel is not as restrictive. The surge section of a vessel is the bottom portion that, during operation will contain a large volume of liquid. Any orientation is possible for a manhole in this section. However, the location of all manholes should be in the back half of the vessel away from the pipe way. The surge section may have a large baffle plate bisecting the diameter of the vessel and extending vertically many feet. A removable plate or hatch may be installed in this baffle (by vessels) to allow access to the far side. The vessel orientation of the manhole should not hit the baffle or be located so close to the baffle that entrance is obstructed.
- Transitions for Coke Bottle Vessels: The cone or transition piece for regular and inverted Coke Bottle vessels may come in the following shapes:
- Flat side: It has a cone is cut from flat plate and formed to a simple cone. There is no knuckle radius at the top or bottom of the cone. The connection to the straight shell of the vessel is an angled weld. Usually there is a reinforcing ring on the shell very close to the shell and cone junction.
- Shaped side: The cone is cut from flat plate and rolled to a shaped cone. There is a knuckle radius at the top and bottom of the cone. The cone has a straight tangent at the top and bottom to match the shells. The connection to the straight shell of the vessel is a common butt weld.
- The other Components include the following:
- Trays: The type of trays, the number of trays, and the number of passes are not the specific responsibility of the piping layout designer. However, there is the need to know about it. A common understanding of terminology will improve communications and prevent errors. The common tray parts are
- Tray support Ring: The tray support ring or Tray ledge is technically not a part of the tray itself. The tray support ring is only there to support the tray. If there are no trays, then there is no need for tray support rings, therefore tray rings are linked to the trays. Tray support rings are normally a simple donut shaped strip welded to the inside of the vessel. They could also be in the shape of an inverted L welded to the vessel wall. Problems arise when the Designer does not allow for the tray support device.
- Tray Deck: One or more sections, consisting of plates, forming a horizontal obstruction throughout all or part of the vessel cross section. The trays will normally be constructed to form one or more flow patterns called passes. The purpose of tray deck is to provide a flow path for the process commodity and contain the fractionation or separation device. A Weir is a low dam on a tray to maintain a liquid level on the tray. Down comer is the primary liquid passage area from higher tray to another lower tray. Valves are also tray hardware device. Bubble Caps is another tray hardware device. Draw off is a way to remove liquid from the vessel. Trough is a way to collect and move liquid from one point to another. Riser is a device to channel vapor from one lower point to a higher point. Seal Pans is a device with a liquid seal that prevents vapors from passing. Beams & Trestles is a devices that support trays or other types of internals in very large diameter vessels. Baffles is a separation device inside a vessel.
- Tray Pass Patterns: The trays and the related down comers can be arranged in a wide verity of patterns. Typical Tray arrangement is Single Pass which is a quite common. This tray pass arrangement has one feed point, one flow direction, and one down comer. The single pass tray will normally be used on small diameter vessels and the smaller diameter of a Coke Bottle vessel. Cross-Flow and Multiple Pass trays come in two pass, three pass, four pass, and on and on. These will normally be found in the larger diameter vessels. Multiple pass trays require multiple feed and draw off arrangements. The more passes, the more complex the orientation problems. Reverse Flow or Single Pass, Radial Flow, Circumferential Flow, Cascade Flow are rare. The single pass tray will have a single down comer. The 2, 3, or 4 pass tray will have the same number of down comers as passes. The number of passes and number of down comers will have a big effect on the orientation. Some towers may have more than one Tray pass configuration. They may have single pass in the top Trays and two-pass Trays in the bottom. The change from one pass configuration to another is chance for error. The alignment of the single pass tray will normally be perpendicular to the two pass trays.
- Tray Types: There is what would be considered Standard Trays, and there are also high efficiency trays. Standard Trays have an open down comer with no separation occurring in the down comer area. This tray is the old stand by and has been used for many years. High efficiency Trays have a sealed down comer with separation occurring in the down comer. This tray type is fairly new. It will most likely be used on most new vessels in the future. It is also the type of tray that is favored on revamp projects to get more out of an existing tower.
- Tray hardware devices: The normal trays inside the typical vertical vessel will contain openings or holes and may be fitted with a fractionation or separation device. This device is what will accomplish the purpose of the vessel. If these devices are not present or do not function properly then the product is not made. There are some common tray devices. Bubble Cap which is used mostly on revamps. Simple, and common method to facilitate the separation process. The Bubble Cap will normally be a round cup shaped cap inverted over a short and smaller diameter chimney. The skirt area of the inverted cap may be plain or have open or closed slots. Box Cap is very much like the common Bubble Cap except it is square. Tunnel Cap will be a long narrow rectangular shape. Uniflux Tray is a series of overlapping and interlocking plates. In cross section the Uniflux tray will have the shape of a reclining squared off. The valve tray is common and has small flat metal plates fitted over the holes in the trays. The plate is loose to move up and down, but is retained in position by a clip type device. Vapor pressure under the valve plate causes it to rise and gravity brings it back down. The second common is sieve tray which has holes and nothing else. The hole size is calculated to provide a fragile balance between the liquid head above the tray and the vapor pressure under the tray.
- Column Internal piping:
- Weirs: There may be a number of places where weirs are used. The simple weir to provide proper tray flooding will normally not cause any design problems. There are also some special purpose weirs that may effect the location of nozzles. In most cases the existence of special purpose weirs will not be known at the start of the Vessel orientation activity.
- Down comers: Down comers can come in a verity of shapes also. They straight across in the horizontal direction, or they can be bent. They can be straight up and down in the vertical direction, they can be sloped, slanted or tapered, or they can be a combination. These variations will all impact the orientation to some extent. The major impact, by the downcomer on the orientation is the geometry or location of the vertical plane itself. The orientation of the down comers will have a direct relationship to the orientation of certain nozzles and manholes.
- Other Tray Terms: Some other terms that will be found relating to trays. Sump is a sealed down comer type area that is designed to provide a retention volume for some purpose. Seal Pans is a portion of a tray that is set deeper than the rest of the tray to form a seal for the down comer from the tray above. Side Draw Tray is an arrangement that allows the removal of a specific liquid product. Chimney Tray is a full circumference tray fitted with long open pipes to allow vapor to pass from below the tray to the space above. Baffles are plates installed in the vessel for a specific purpose. Impingement Plates are somewhat like a baffle but normally a plate installed in the vessel at the inlet to prevent blowout to devices located on the opposite side of the vessel. Tray manholes are there in most, if not all, trays, where it will have a removable panel somewhere in the tray to allow inspection passage without dismantling the total tray.
- Vessel Support: There is a wide variety in the methods used to support vessels. Each of these support types may also have variations. The tall towers are generally supported by skirts. Horizontal storage tanks are supported by integral steel saddles. Reactors are supported on lugs. Receivers and feed tanks are supported on legs or are portable on casters. Pads are welded on vessels which are supported on concrete saddles. Direct bury method is used for underground tanks. The method of vessel support depends on various factors. These factors include process function, operation access, maintenance clearances, ease of constructability, and cost. Meeting the positive criteria for all or the majority of these factors will drive the support method. Each of these vessel support methods has their own good points and bad points. The Tall Skirt is the most common because it meets more of the preferred criteria than the others do. The primary methods of support are Skirts. Tall Skirt on foundation at grade are most common. Short Skirt on elevated pier foundation, table support, or structure. The minimum height of the skirt is normally set by process based on the Net Positive Suction Head requirements of the pumps or for the reboiler hydraulic requirements. The designer may need to increase the skirt height due to vertical distance required by pump suction line geometry, Vertical distance required by reboiler line geometry, Operator aisle headroom clearance, and suction line entering the pipe rack without pockets. The approval of the Process engineer, Project Manager, and the Client will be required for any increase to the skirt height. The skirt will have one or more access openings and will have skirt vents. Skirts of vessels in refineries or other plants processing flammable commodities will normally be fireproofed. The fireproofing is normally a two inch thick layer of a concrete type material applied to the outside of the skirt. Check for the specific type. Some materials may require up to 6 inch to obtain the required fire rating. Legs can be installed on foundation at grade. Lugs on vessels can be put on elevated pier foundation, table support, or structure.
- Load Handling Devices: Load handling devices are required for Vertical Vessels if the vessel is over thirty feet tall or the vessel has removable trays and internals. The vessel has components like Pressure Safety Valves, control valves which require frequent removal for routine maintenance and if the components weigh 100 pounds or more. Davit is a small somewhat inexpensive device used for lifting and supporting heavy objects up and down from elevated platforms. Limited to a fixed reach. Monorail is a more expensive method, which is a girder provided along floor ceiling. Crane is a far more expensive method and is dependent on availability. If a davit or monorail is not installed then a crane with the required reach and load rating must be rented or an alternate method must be jury-rigged. Any jury rig method will have a high potential for accident and injury. When a Davit is to be included the location, swing, the clearance height including lifting device, the reach of the removal items, and maximum load of external items must be determined and furnished. When a Monorail is to be included the platform, and monorail support configuration, the clearance height including lifting device, the reach to the drop zone, the maximum load of external items where vessels will determine weight of internals, must be determined and furnished to the Vessels engineer.
- Pipe supports and Guides: The Pipe Supports and Pipe Guides for the piping that is attached to the vessel is the responsibility of the Piping Group. You are the Piping engineer and you need to make sure it is properly supported and guided. The rule is that all lines shall be properly supported and guided. One key element of the Pipe Supports and Pipe Guides is the L dimension. The L dimension is the distance from the outer diameter of the back side of the pipe to the outer diameter of the vessel. This dimension should be as small as possible but not less than required for maintenance. The rule of thumb for the L dimension is 12 inches minimum and 20 inches maximum. Dimensions of under the 12 inches and over the 20 inches are sometimes allowed. For example, if fitting make up results in an L dimension of 12 inches do not add a spool piece and extra weld. Lines should be supported as close to the nozzle as possible. The type of support is based on the weight of what is being supported. It may be just a straight pipe dropping down the side of the vessel. Or, it may be much more. Pipe supports attached to a vessel must be evaluated for the shell thickness, orientation, elevation, the L dimension, the weight of the basic pipe and fittings based on size and wall schedule, the weight of the water during hydro test, the weight of the insulation if any, the weight of any added components such as block valves, control valve stations, relief valves, etc. There should be clearance to other objects like seams, Stiffener rings, Nozzles, Clips, Pipe Lines, Platforms. Pipe supports and guides should be staggered vertically for clearance from supports or guides on other lines running parallel.
- Platforms, Ladders, and Cages: Platforms with access ladders must be provided as required for access to manholes, operating valves, and instruments as defined in the project criteria. Normally objects below 15 feet from grade will not require permanent platforms and ladders. These objects are judged assessable by portable means. Check the Project design requirements. Platform spacing shall be even foot increments when multiple platforms are serviced from a single ladder. The platforms shall be arranged to allow a minimum 7 feet headroom to underside of any obstruction, minimum 2 feet 6 inches radial width for primary egress path which is inside distance of platform to outside distance of platform, minimum 2 feet 6 inches clear distance between ladders. There should be no obstructions in path between primary egress ladders. Maximum 30 feet vertical travel length of ladder should be between platforms. Side step off at all platforms which is step through ladders, are considered dangerous and therefore should be avoided. This requirement should have been reviewed with the Client and defined in the Design Criteria. Combining with platforms on other vessels when potential for improved operations or maintenance exists. Flanges of top head nozzles shall be extended to provide access to bolts. Minimum 1 foot 6 inches clearance around objects if for maintenance access only.
- Code Name Plate: Every vessel will have a Code Name Plate. On a vertical vessel the code name plate must be on the pressure containment part of the shell. It cannot be attached to the skirt. The best place for the code name plate on a vertical vessel is 2 feet 6 inches above the horizontal centerline of the surge section manhole. Make sure the location selected is accessible on grade or on a platform.
- Vertical Tower: Normally vessel components are described using common terms such as shell, head, nozzle, and support. Some vessels will also have special terms based on function. Typical special terms include the following. Flash Section is the area or zone of the fractionation vessel where the primary feed enters the vessel. Fractionation Section is the portion of the vessel that includes the trays. Stripping Section is a place in the vessel that includes the introduction of supplementary heat such as high temperature steam. Surge Section is the bottom portion of the vessel that normally includes the main outlet nozzle, which is connected to the bottoms pumps.
- Common problems with vertical vessels: Most important is schedule crunch. Vessels scheduled for purchase too early requiring firm orientations with very little backup information. The information required is approved and issued documents for Design P & I D, Exchanger type and location, flare header and location of pressure safety valves. Thin wall vessels not able to support load on pipe supports. High wind presence requiring extra guides. Late changes to pressure safety valve sizing, prompts changes to pipe support and guides on line to flare. Late change to control valve location criteria, due to which flashing service are required to be located to elevated platform on vessel, with line downstream of valve self drain to vessel. Reboilers requiring spring mounted supports have to be moved due to tight piping and differential growth. High steam out temperature requires extra flexibility in the piping. Extra heavy object removal is difficult if there is increase in excess load of Davit load capabilities.
- Vertical Vessel Orientation: The ladder approach at grade should be free of obstructions and easily accessible. Verify preferred location with Project requirements. The Manhole orientation should be oriented in the back half of the vessel toward the access way. The manholes should be arranged with consideration to the type of load handling device. You should maintain one centerline if monorail is used, one or two centerlines if davit is used, no specific restriction if crane. Load drop area should be located on the main access side. Level instruments should be located on or near the front half of the vessel and visible from the main operating aisle. The piping risers to and from the vessel should be located to the front half of the vessel for easy routing to the pipe way and equipment.
- Manholes: Manholes will influence the entire vessel orientation to a certain degree. The location of the manholes must be compatible with the location of the tray down comers. The down comers in turn influence the location of the process and instrument nozzles. The preferred elevation of manholes above the platform is 2 feet 6 inches from the centerline. The limits are minimum 6 inches from the top of the platform to the bottom of the flange, or maximum 4 feet from the top of the platform to the bottom of the flange. Verify preferred location with Project requirements. Platforms may not be required for manholes that are 15 feet or less above grade, unless a platform is required for another reason such as an instrument. Verify preferred location with Project requirements. Space and clearances are important around manholes. Check flange swing and tray lay down space.
- Ladders and Platforms: Check to see that the approach to the ladder at grade is clear of all obstructions and hazards, the entry onto each platform is clear and not blocked by level or other instruments, the entry onto each platform is clear and not blocked by an open manhole flange, there is a clear path from one down ladder to the next down ladder for unobstructed travel during emergencies. Platforms may need to be added or extended for access to operating valves, spec blinds, or instruments. Special platforms are often required at the channel end of a thermo-siphon reboiler or other equipment that is mounted directly into or onto the vessel. Investigate lining up and connecting platforms servicing equipment, such as Reboilers or Accumulators, which are located in adjacent structures but related to the vessel. Maintenance criteria at Reactors often require platforms large enough and strong enough for large flange or head lay down in addition to catalyst storage and handling. Check the location and size of the pipe penetration holes through platforms. The opening is to be one inch larger in diameter than the flange or pipe plus insulation, which ever is greater. Provide proper routing and support for all lines regardless of size. Do not route small lines vertically behind the ladders. Do not route small lines vertically between the vessel shell and the inside radius of the platforms. Do not route small lines vertically up the outside of the platforms in line with or close to the manholes. Ladder access openings must be fitted with a safety gate. Check for proper clearance for gate swing. Some processes are subject to periods of hazardous operations. Ladders and ladder cages may need to be designed for operators with self-contained suits and air packs.
- Reboilers: Reboilers will be either Fired or Heater Type, Thermosiphon which can be vertical or horizontal shell & tube type, or Kettle type which can be horizontal shell & tube type. Fired Reboilers shall be located a minimum of fifty feet from the vessel. Piping to and from any type of reboiler will be hot, and have sensitive flow conditions. The Kettle or Thermosiphon Reboiler elevation is set by Process and indicated on the P & I D.
- Pipe Supports and Guides: Piping is responsible for locating the pipe supports and guides on vessels and for defining the size and loads on the pipe supports on vessels.
- Piping Flexibility: Piping must determine the operating thermal growth of the vessel. The vessel will have a series of temperature zones from the bottom to the top. The differential expansion between the piping risers and the vessel must be checked to prevent over stressing the piping or the vessel shell. The routing of cooler reflux lines must consider the total growth of the hotter vessel. Potential for differential settlement needs to be investigated. Each piping system or line needs to be considered individually.
- Instrumentation: The high and low level alarms need to be carefully considered because they will set the elevations of the level instruments. Orientation of level instrument connections needs to consider the internals. All instruments shall be accessible. Watch out for space requirements for gage glass illuminators. Temperature indicators and thermo well connections will require removal space.
- Electrical: Space shall be allocated for conduit runs up the vessel. These conduits will carry power to platform lights, gage glass illuminators, and in some cases electrical tracing. Conduits are also required for controls and for instrumentation cables.
- Piping Valves: Valves are meant to be operated. To operate them, they must be accessible. 2 inch and smaller valves may be considered accessible from a platform or ladder. 3 inch and larger valves shall be accessible on a platform.
- Miscellaneous Piping issues: Lines to and from vessels may be subject to conditions such as 2 phase flow or vacuum. Some Pressure Safety Valves relieving to atmosphere will require snuffing steam. The steam pressure in the line must be adequate to reach the top of the vessel. Large overhead lines verses location of Pressure Safety Valves, require special attention for function and support. Vertical vessel piping needs to be checked for heat tracing requirements. A tracer supply manifold may need to be added at the top of the vessel.
- Ease in Construction: All vertical vessels shall be reviewed for ease in construction. This review needs to consider receiving logistics lay down orientation, lifting plan, pre-lift assembly items. Pre-lift assembly items may include Piping, Platforms, Ladders, Internals, Paint, Insulation.
- Fire Protection: Some vessels may require special insulation for fire protection, fire monitor coverage and sprinkler systems.
- Lined Vessels: Some vessels will be lined. Linings may be metallic, plastic, or glass. Welding to the vessel shell after initial fabrication is not allowed. Some vessels will have flanged connections that are larger than 24 inches. These connections will occur at connections for piping, reboilers, or other equipment. Flanged connections over 24 inches do not have a single standard and need to be defined for specific type.
- Maintenance Aisles at grade: Equipment maintenance aisle for hydraulic crane with a 12 Ton capacity should have a minimum horizontal clearance width of 10 foot or 3 meters and a minimum vertical clearance of 12 foot or 3.5 meters. Where a fork lift and similar equipment of 5,000 pounds or 2300 kilograms capability, is to be used the minimum horizontal clearance should be 6 foot or 2 meters and the minimum vertical clearance should be 8 foot or 2.5 meters. Where maintenance by portable manual equipment like hand trucks, dollies, portable ladders or similar equipment, is required the minimum horizontal clearance should be 3 foot or 1 meter and the vertical clearance 8 foot or 2.5 meters. Operating Aisle at grade should have a minimum width of 2 foot or 800 millimeters and a headroom of 7 foot or 2.1 meters.
- Supporting Equipment:
- Flare Stacks: Locate the flare stack upwind of process units, with a minimum distance of 200 feet or 60 meters from process equipment, tanks, and cooling towers. If the stack height is less than 75 feet or 25 meters, increase this distance to a minimum of 300 feet or 90 meters. These minimum distances should be verified by Company Process Engineering.
- Furnaces: Locate fired equipment, if practical, so that flammable gases from hydrocarbon and other processing areas cannot be blown into the open flames by prevailing winds. Shell to shell horizontal clearance from hydrocarbon equipment should be 50 foot or 15 meters with the exception of reactors or equipment in alloy systems which should be located for economical piping arrangement. Provide sufficient access and clearance at fired equipment for removal of tubes, soot blowers, air pre-heater baskets, burners, fans, and other related serviceable equipment. Clearance from edge of roads to shell should be 10 foot or 3 meters. Pressure relief doors and tube access doors should be free from obstructions. Orient pressure relief doors so as not to blow into adjacent equipment. The elevation of the bottom of the heater above the high point of the finished surface, should allow free passage for operation and maintenance. In case of furnace piping, locate snuffing steam manifolds and fuel gas shut off valves at a minimum distance of 50 feet or 15 meters horizontally from the heaters they protect. Burner valves for a floor fired furnaces should be a combination of oil and gas firing valves. It should be operable from burner observation door platform. For those fired by gas only, the valves should be near the burner and should be operable from grade. Burner valve for a side fired furnaces should be so located that they can be operated while the flame is viewed from the observation door.
- Heat Exchangers: Heat exchangers come in a variety of designs. In a process facility shell and tube exchangers are the most common and are manufactured in accordance with the Tubular Exchanger Manufacturers Association code. The most common type of industrial heat exchanger is the shell and tube type where one stream, usually the one that leaves the most deposit like cooling water, flows through the tubes and the other stream goes through the shell side. This is because the tubes are easier to clean than the shell. Provision must be made to withdraw the tubes for cleaning and this area must be kept free of piping and other obstructions. Shell and tube exchangers are manufactured in accordance with the Tubular Exchanger Manufacturers Association code.
- Shell and Tube Exchangers: Shell and tube exchangers should be grouped together wherever possible. Keep channel end and shell covers clear of obstructions such as piping and structural members to allow unbolting of exchanger flanges, and removal of heads and tube bundles.
- Stacked Shell and Tube Exchangers: Stacked shell and tube exchangers should be limited to four shells high in similar service; however, the top exchanger should not exceed a centerline elevation of 18 feet or 5.5 meters above high point of finished surface, unless mounted in a structure.
- Maintenance Requirements: Exchangers with removable tube bundles should have maintenance clearance equal to the bundle length plus 5 feet or 1.5 meters measured from the tube sheet to allow for the tube bundle and the tube pulling equipment. Minimum maintenance space between flanges of exchangers or other equipment arranged in pairs should be 1 foot 6 inches or half meter. Exchanger maintenance space from a structural member or pipe should not be less than 1 foot or 300 millimeters.
- Piping at Shell and Tube Exchangers:
- Reboilers: Locate kettle reboilers at grade and as close as possible to the vessel they serve. This type of reboiler is identifiable by its unique shape. It has one end much like a normal Shell and Tube exchanger then a very large eccentric, bottom flat transition to what looks like a normal horizontal vessel. You could also call it a Fat exchanger. The flow characteristics on the process side of a kettle reboiler are the reason for the requirement for the close relationship to the related vessel. Reboilers normally have a removable tube bundle and should have maintenance clearance equal to the bundle length plus 5 feet or 1.5 meters measured from the tube sheet.
- Double Pipe Exchangers: These exchangers can be mounted almost anywhere and with process engineer approval, they can be mounted in the vertical when required. A G-Fin Exchanger is recognizable by its shape. One segment looks like two long pieces of pipe with a 180 degree return bend at the far end. It is one finned pipe inside of another pipe with two movable supports. This type of exchanger can be joined together very simply to form multiples in series, in parallel or in a combination of series or parallel to meet the requirements of the process. This exchanger is not normally used in a service where there is a large flow rate or where high heat transfer is required. The key feature with this exchanger is the maintenance. The piping is disconnected from the tube side, which is the inner pipe. On the return bend end of this exchanger there is a removable cover. When the cover is removed this allows for the tube, or inside pipe to be pulled out. This exchanger is normally installed with the piping connections toward the pipe rack.
- Plate Heat Exchangers: A plate heat exchanger is a type of heat exchanger that uses metal plates to transfer heat between two fluids. This has a major advantage over a conventional heat exchanger in that the fluids are exposed to a much larger surface area because the fluids spread out over the plates. This facilitates the transfer of heat, and greatly increases the speed of the temperature change. Plate heat exchangers are now common and very small brazed versions are used in the hot-water sections of millions of combination boilers. The high heat transfer efficiency for such a small physical size has increased the domestic hot water flow rate of combination boilers. The small plate heat exchanger has made a great impact in domestic heating and hot-water. Larger commercial versions use gaskets between the plates, smaller version tend to be brazed. The concept behind a heat exchanger is the use of pipes or other containment vessels to heat or cool one fluid by transferring heat between it and another fluid. In most cases, the exchanger consists of a coiled pipe containing one fluid that passes through a chamber containing another fluid. The walls of the pipe are usually made of metal, or another substance with a high thermal conductivity, to facilitate the interchange, whereas the outer casing of the larger chamber is made of a plastic or coated with thermal insulation, to discourage heat from escaping from the exchanger.
- Fin Fans (Air Coolers): Air Coolers are in typically used in the cooling of the overhead vapor from tall vertical vessels or towers such as Crude Fractionators and Stripper Columns. The natural flow tends to follow gravity, where the tower overhead is the high point then down to the Air Cooler, then down to the Accumulator and finally the Overhead Product transfer pumps. With this in mind the Air Coolers are normally located above pipe ways. This conserves plot space and allows the pipe rack structure with it's foundation to do double duty with only minor up grade to the design. If the pipe rack is not used then plot space equal to the size of the Air Cooler is required. In addition a totally separate foundation and stand alone structure is required. Air coolers, or fin fans, are utilized globally in modern process facilities. Air is quickly moved past the tube exterior by way of a large fan system. As the product travels through the tubes, this process transfers the heat from the product into the atmosphere. An air cooler or fin fan unit is constructed of several hundred to several thousand externally finned tubes. Tube dimensions typically range from 1 inch or 25.4 millimeters to 1.5 inch or 38 millimeters in diameter and up to 75 feet or 23 meters in length.
- Storage Tanks: A storage tank is a container, usually for holding liquids, sometimes for compressed gases, called as gas tank. The term is used for manufactured containers. Storage tanks operate under no or very little pressure, distinguishing them from pressure vessels. Storage tanks are often cylindrical in shape, perpendicular to the ground with flat bottoms, and a fixed or floating roof. There are usually many environmental regulations applied to the design and operation of storage tanks, often depending on the nature of the fluid contained within. Aboveground storage tanks differ from underground storage tanks in the kinds of regulations that are applied. Storage tanks are available in many shapes, vertical and horizontal cylindrical, open top and closed top, flat bottom, cone bottom, sloping bottom and dish bottom. Large tanks tend to be vertical cylindrical, or to have rounded corners with transition from vertical side wall to bottom profile, which makes it to easier withstand hydraulic pressure of contained liquid. Most container tanks for handling liquids during transportation are designed to handle varying degrees of pressure. A large storage tank is sometimes mounted on a lorry or on an articulated lorry trailer, which is then called a tanker.
- Horizontal Drums: Horizontal vessels and drums are relatively large diameter cylindrical pressure vessels used for a variety of process functions. Their height above grade is usually determined by the Net Positive Suction Head requirements of the pumps in the liquid outlet line or the gravity flow requirements to other equipment. And they are supported by the use of saddles. Some vessels have Boots and Weirs. These accumulate water coming in the drum with hydrocarbons and water is drained out continuously or from time to time. Nozzle Orientation depends on the service. Inlets are from top. Outlets are from bottom and level gage is put on nozzles on side. Platforms are used to operate valves on top nozzles. Horizontal Drums are separated from each other by at least 4 feet or 1 meter and are located inside a dyke wall.
- Vertical Tanks: Usually cylindrical they vary greatly in size from 2 feet to 200 feet diameter mostly flat bottomed with either an open or conical top, some of the large tanks used in refineries have a floating top where the roof floats on top of the liquid to eliminate vapor loss. Tank Roofs can be conical or dished. Flat roofs are not used. There are floating roofs for crude oil and gas storage. Small tanks are installed on concrete foundations while large tanks are placed on soil, called as mud foundation. Stairs and Ladders are provided to go up to the roof. Spiral stairs are provided for large diameter tanks while Ladders are provided for small diameter tanks. Large tanks are separated from each other by at least 20 feet or 5 meters and are located inside separate dyke walls. Small tanks are separated from each other by at least 4 feet or 1 meter and are located inside a common dyke wall. Dyke volume is designed to hold entire quantity of liquid inside the dyke wall, in case the tank ruptures. Fire Protection equipments are provided around the dyke wall. Offsite piping is generally mounted on grade. Tanks generally have inlet, outlet, recirculation and vent piping. Locate vertical vessels in the equipment rows on each side of the pipe way in a logical order based on the process and cost. The largest vessel in each equipment row should be used to set the centerline location of all vertical vessels in that equipment row. This largest vertical vessel should be set back from the pipe rack a distance that allows for pumps, the pump piping, an operation aisle between the pump piping and any piping in front of the vessel, the edge of the vessel foundation and half the diameter of this the largest vessel. Provide a clear access area at grade for vessels with removable internals or for vessels requiring loading and unloading of catalyst or packing. Provide vessel davits for handling items such as internals and relief valves on vessels exceeding a height of 30 feet or 9 meters above the high point of the finished surface, and on vessels not accessible by mobile crane. Orient davits to allow the lowering of appurtenances into the access area.
- Pressure Vessels: A pressure vessel is a closed container designed to hold gases or liquids at a pressure substantially different from the ambient pressure. Many of the reaction vessels are pressure vessels. These have jackets or limpet coils to circulate heating or cooling media. The contents of the vessel are mixed by agitators. The pressure differential is dangerous and many fatal accidents have occurred in the history of their development and operation. Consequently, their design, manufacture, and operation are regulated by engineering authorities backed up by laws, such as ASME Section 8. For these reasons, the definition of a pressure vessel varies from country to country, but involves parameters such as maximum safe operating pressure and temperature. Pressure vessels are used in a variety of applications in both industry and the private sector. They appear in these sectors as industrial compressed air receivers and domestic hot water storage tanks. Other examples of pressure vessels are: diving cylinder, recompression chamber, distillation towers, autoclaves and many other vessels in mining or oil refineries and petrochemical plants, nuclear reactor vessel, habitat of a space ship, habitat of a submarine, pneumatic reservoir, hydraulic reservoir under pressure, rail vehicle airbrake reservoir, road vehicle airbrake reservoir and storage vessels for liquefied gases such as ammonia, chlorine, propane, butane. Pressure vessels may theoretically be almost any shape, but shapes made of sections of spheres, cylinders, and cones are usually employed. A common design is a cylinder with hemispherical end caps called heads. More complicated shapes have historically been much harder to analyze for safe operation and are usually far more difficult to construct.
- Pumps: A centrifugal pump is a kinetic machine converting mechanical energy into hydraulic energy through centrifugal activity. A centrifugal pump is one of the simplest pieces of equipment. Its purpose is to convert energy of an electric motor or engine into velocity or kinetic energy and then into pressure of a fluid that is being pumped. The energy changes occur into two main parts of the pump, the impeller and the volute. The impeller is the rotating part that converts driver energy into the kinetic energy. The volute is the stationary part that converts the kinetic energy into pressure. Liquid enters the pump suction and then the eye of the impeller. When the impeller rotates, it spins the liquid sitting in the cavities between the vanes outward and imparts centrifugal acceleration. As the liquid leaves the eye of the impeller a low pressure area is created at the eye allowing more liquid to enter the pump inlet. Provide temporary conical type strainers in 2 inch or 50 millimeters and larger butt weld pump suction lines for use during startup. Arrange piping to facilitate removal. Use permanent Y-type strainers on 2 inch or 50 millimeters and smaller screwed or socket weld pump suction piping.
- Centrifugal Pumps: A centrifugal pump is a rotary dynamic pump that uses a rotating impeller to increase the pressure of a fluid. Centrifugal pumps are commonly used to move liquids through a piping system. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially, outward into a diffuser or volute chamber casing, from where it exits into the downstream piping system. Centrifugal pumps are used for large discharge through smaller heads. A centrifugal pump works by converting kinetic energy into potential energy measurable as static fluid pressure at the outlet of the pump. This action is described by Bernoulli's principle. With the mechanical action of an electric motor or similar, the rotation of the pump impeller imparts kinetic energy to the fluid through centrifugal force. The fluid is drawn from the inlet piping into the impeller intake eye and is accelerated outwards through the impeller vanes to the volute and outlet piping. As the fluid exits the impeller, if the outlet piping is too high to allow flow, the fluid kinetic energy is converted into static pressure. If the outlet piping is open at a lower level, the fluid will be released at greater speed.
- Multistage Centrifugal Pumps: A centrifugal pump containing two or more impellers is called a multistage centrifugal pump. The impellers may be mounted on the same shaft or on different shafts. If we need higher pressure at the outlet we can connect impellers in series. If we need a higher flow output we can connect impellers in parallel. All energy added to the fluid comes from the power of the electric or other motor force driving the impeller.
- Pump Piping: A pump normally has a suction line and a discharge line. Suction line should not have any bends in it and should be one size bigger than the pump suction nozzle size. A block valve and a strainer is generally installed in suction line. To allow this, suction line should be at least 3 feet or 1 meter long. The discharge line generally originates from top of pump. A check valve, and a pressure gage assembly is generally installed in this line. It should not disturb in removal of pump from foundation.
- Cavitation: Within a centrifugal pump, the flow area at the eye of the pump impeller is usually smaller than either the flow area of the pump suction piping or the flow area through the impeller vanes. When the liquid being pumped enters the eye of a centrifugal pump, the decrease in flow area results in an increase in flow velocity accompanied by a decrease in pressure. The greater the pump flow rate, the greater the pressure drop between the pump suction and the eye of the impeller. If the pressure drop is large enough, or if the temperature is high enough, the pressure drop may be sufficient to cause the liquid to flash to vapor when the local pressure falls below the saturation pressure for the fluid being pumped. Any vapor bubbles formed by the pressure drop at the eye of the impeller are swept along the impeller vanes by the flow of the fluid. When the bubbles enter a region where local pressure is greater than saturation pressure farther out the impeller vane, the vapor bubbles abruptly collapse. This process of the formation and subsequent collapse of vapor bubbles in a pump is called cavitation. Cavitation in a centrifugal pump has a significant effect on pump performance. Cavitation degrades the performance of a pump, resulting in a fluctuating flow rate and discharge pressure. Cavitation can also be destructive to pumps internal components. When a pump cavitates, vapor bubbles form in the low pressure region directly behind the rotating impeller vanes. These vapor bubbles then move toward the oncoming impeller vane, where they collapse and cause a physical shock to the leading edge of the impeller vane. This physical shock creates small pits on the leading edge of the impeller vane. Each individual pit is microscopic in size, but the cumulative effect of millions of these pits formed over a period of hours or days can literally destroy a pump impeller. Cavitation can also cause excessive pump vibration, which could damage pump bearings, wearing rings, and seals. A small number of centrifugal pumps are designed to operate under conditions where cavitation is unavoidable. These pumps must be specially designed and maintained to withstand the small amount of cavitation that occurs during their operation. Most centrifugal pumps are not designed to withstand sustained cavitation. Noise is one of the indications that a centrifugal pump is cavitating. A cavitating pump can sound like a can of marbles being shaken. Other indications that can be observed from a remote operating station are fluctuating discharge pressure, flow rate, and pump motor current.
- Pump Curves: It gives the Best Efficiency Point, which is the point at which effects of head or pressure and flow converge to produce the greatest amount of output for the least amount of energy. For a specified impeller diameter and speed, a centrifugal pump has a fixed and predictable performance curve. The point where the pump operates on its curve is dependent upon the characteristics of the system, in which it is operating, commonly called the System Head Curve, or the relationship between flow and hydraulic losses in a system. This representation is in a graphic form and, since friction losses vary as a square of the flow rate, the system curve is parabolic in shape.
- Pump Location and Layout: If available floor area is limited, a vertical unit generally requires less area. However, if available headroom is limited the horizontal unit almost invariably requires less headroom. It should be kept in mind that area and height requirements will differ somewhat between various manufacturers and with the type of configuration of the unit specified.
- Vertical Inline Pumps: Vertical Inline Close Coupled Pumps are specifically designed for mounting, in any position, directly in a pipe line. The suction and discharge nozzles are located on the same centerline 180 degrees apart. Vertical pumps significantly reduce the space required, two pumps fit in the space of one. They are easy to maintain; simply remove the cap screws and the motor and bracket assembly is easily removed from the casing without disturbing the piping. The impeller is direct coupled to the motor shaft for easy maintenance to minimize impeller run out and reduce noise. Most pump parts except for the casing, are 100% interchangeable. The inline casing has provisions for mounting an optional support base should the pump sit on the floor. Mechanical seals can be provided as standard to prevent leakage around the shaft. A relief line may be provided from the seal faces to the pump discharge for flushing and venting purposes. Suction Branch Design pre-rotates suction liquid in the direction of pump impeller rotation. This concept minimizes pumping noise that is otherwise associated with more common short radius suction inlet designs.
- Compressor: A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume. Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas. Liquids are relatively incompressible, so the main action of a pump is to transport liquids.
- Reciprocating Compressor Piping: Locate reciprocating compressors in such a position, so that suction and discharge lines that are subject to mechanical and acoustical vibration may be routed at grade and held down at points established by a stress and analog study of the system. Accessibility and maintenance for large lifts such as cylinder, motor rotor, and piston removal should be by mobile equipment if the installation is outdoors or by traveling overhead crane if the installation is indoors or covered. Horizontal, straight line, reciprocating compressors should have access to cylinder valves. Access should be from grade or platform if required. Depending on unit size and installation height, horizontal-opposed and gas engine driven reciprocating compressors may require full platform at the operating level.
- Centrifugal Compressor Piping: Locate centrifugal compressor as close as possible to the suction source. Top suction and discharge lines should either be routed to provide clearance for overhead maintenance requirements, or should be made up with removable spool pieces. Support piping so as to minimize dead load on compressor nozzles. The load should be within the recommended allowance of the compressor manufacturer. Centrifugal compressors should have full platform at operating level. Heavy parts such as upper or inner casing and rotor should be accessible to mobile equipment. Review the equipment arrangement for access and operation. Locate lube and seal oil consoles adjacent to and as close as possible to the compressor. Oil return lines from the compressor and driver should have a minimum slope of half inch per foot to the inlet connection of seal traps, degassing tanks, and oil reservoir. Pipe the reservoir, compressor bearing, and seal oil vents to a safe location at least 6 feet above operator head level.
- Control Valve Stations: Locate control valve stations accessible from grade or on a platform. In general, the flow, level, pressure and temperature instruments or indicators showing the process variables should be visible from the control valve.
- Cooling Towers: Locate cooling towers downwind of buildings and equipment to keep spray from falling on them. Orient the short side of the tower into the prevailing summer wind for maximum efficiency. This means that the wind will travel up the long sides and be drawn in to both sides of the cooling tower equally. When the wind is allowed to blow directly into one long side it tends to blow straight through and results in lower efficiency. Locate cooling towers a minimum of 100 feet or 30 meters from process units, utility units, fired equipment, and process equipment.
- Steam Boiler: A boiler is a closed vessel in which water is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications. The pressure vessel in a boiler is usually made of steel or alloy steel. Stainless steel is virtually prohibited by the ASME Boiler Code for use in wetted parts of modern boilers, but is used often in super heater sections that will not be exposed to liquid boiler water. There are two main types of boilers. Fire tube boiler, is one where, water partially fills a boiler barrel with a small volume left above to accommodate the steam. This type of boiler not used in industry. In Water-tube boiler, the water tubes are arranged inside a furnace in a number of possible configurations, often the water tubes connect large drums, the lower ones containing water and the upper ones, steam and water. In small boilers, such as a mono tube boiler, water is circulated by a pump through a succession of coils. This type generally gives high steam production rates, but less storage capacity than the above. Water tube boilers can be designed to exploit any heat source and are generally preferred in high pressure applications, since the high pressure water or steam is contained within small diameter pipes which can withstand the pressure with a thinner wall. Boiler is generally located in utility area, away from process plant.