Design calculations for hot water pump room

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Postscript to the Design of the Hot Water Pump Room at Xi Liu 10 Station Abstract: The hot water pump room plays a relatively important role in the process design of surface facilities in oil and gas fields. Apart from purchased equipment and numerous pipelines, pumps are the main components that drive the operation of these systems. This paper selects the model of the hot water pump by calculating its flow rate and head ； It also provides a relatively detailed discussion on the selection, calculation, and installation of pipelines, equipment, and containers in the hot water pump room. Keywords: Equipment selection calculation, Installation dimensions, Hot water pump room, Design 1 Introduction to the design 1.1 Overview of the hot water pump room design This hot water pump room design is part of the renovation and expansion project for Station 10 in Xiliu. In accordance with the adjustment plan for the flow direction of crude oil in the western Renqiu oil field, Station Xiliu 10 has been switched from transporting high-quality oil to transporting oil containing water; it now transports this oil to Yanyi Combined Station for processing, instead of sending it to Rener II Combined Station via the Gaoren pipeline ； Additionally, 19 more oil production wells were added, which increased the heat consumption at Station Xi Liu 10. The existing heat supply was insufficient to meet the production needs, so a new hot water pump room had to be constructed; once completed, it would replace the old one. 1.2 Site Location and Natural Conditions Station Xi Liu 10 is located near Xiaowangguozhuang in Gaoyang County, Baoding City, Hebei Province, and falls under the jurisdiction of the First Oil Production Plant of the North China Oilfield Branch. Gaoyang County is located on a vast plain and has a temperate continental monsoon climate. The annual sunshine duration ranges from 2,400 to 3,100 hours, the frost-free period lasts from 120 to 200 days, and the average annual precipitation is between 300 and 800 mm. The average monthly temperature is below 3°C, while the average temperature in July is between 18°C and 27°C. The four seasons are well-defined here. 2 Design Content 2.1 Calculation of frictional losses from the transfer station to the metering station and then to individual wells The oil systems in West Liu Station, from the transfer station to the metering station and from the metering station to individual wells, all adopt a three-pipe heat tracing design. 2.1.1 Friction loss from individual wells to the metering station: Since the various wells are connected in parallel, when calculating this friction loss, the water circulation rate per well is taken as 2 t/h. The maximum distance from a single well to the metering station is 1 km; the three-pipe heat tracing system is shown in Figure 1. Figure 1: Schematic diagram of the three-tube heat tracing system. Here, the fluid is in a mixed-friction zone; the hydraulic friction coefficient can be calculated using the following formula, from which the friction loss for the heated return water can be determined. 2.1.2 Friction loss between the transfer station and the metering stations: The metering stations are considered to have a maximum of 11 individual wells each. Since these metering stations are connected in parallel, the friction loss is calculated based on the farthest one among them. The maximum distance between the transfer station and the metering station is 1.2 km. Here, the fluid is in a mixed-friction zone; the hydraulic friction coefficient can be estimated using the following formula: , resulting in a friction loss due to heat return water of . Assuming a loss within the station when hot water enters and exits the transfer station to be 25 m, the total friction loss is . 2.2 Calculation of hot water pump displacement and head: Station Xi Liu 10 currently has 1 crude oil heater with a capacity of 683 kW, and 2 hot water heaters with a capacity of 2330 kW each. The internal heat load at Xiliu Station 10 mainly includes heat required for production and daily activities. Based on the temperatures during the coldest month of winter, the heat loads for each category are as follows: 1) The current total number of oil wells in operation is 54, with 15 additional wells, giving a total of 69 wells. Assuming a heat load of 46.5 kW per well, the total heat load required for the oil wells is 3208.5 kW. 2) Add 1 new oil-to-water heat exchanger at the head office (heat exchange area F=200 m2, plate-type heat exchanger), with a heat load of 574 kW ； 2 new external heat exchangers have been added (heat exchange area F=200 m2; floating-head heat exchangers), with a heat load of 670 kW each ； There is 1 heating and heat exchange unit for oil incoming at Gaoyang Station (heat exchange area F=200 m2, floating-head heat exchanger), with a thermal load of 509 kW. Then the total heat load required by the heat exchanger is 1753 kW. 3) An additional 300 m3 accident oil storage tank is to be added, with a required heat load of 27 kW ； The original 200 m3 oil tank required a heat load of 21 kW ； The heat load for internal heating and insulation in the station is 582 kW; therefore, the total heat load required for heating within the station as well as for insulating the equipment pipelines is 630 kW. The total heat load throughout the entire plant is 5592 kW (equivalent to 480.8×104 kcal/h). Considering a temperature difference of 20°C between the inlet and outlet of the heating furnace, estimate the flow rate required for the hot water pump. G = Q/(CΔt) = 480.8×104/(1×20) = 240 (m3/h). Two hot water pumps have been installed at Station 10 in Xiliu, with a flow rate of qv = 100 m3/h and a head of h = 100 m. After further calculations (qv = 120 m3/h, h = 115 m), it was found that the head and flow rate of these hot water pumps are insufficient to meet the production requirements; therefore, modifications are necessary. Therefore, 3 new hot water pumps will be installed (2 in operation and 1 as backup), with the model and specifications as follows: PAC80-400B, qv=130m3/h, h=80m～155m, motor power P=110kW, shaft power 92kW. There is also 1 return water tank with a capacity of 20 m3, which needs to be replaced due to years of wear and tear. 2.3 Calculation for selecting the diameter of hot water pump pipes – Determining the appropriate diameter of the inlet and outlet manifolds for hot water pumps is an important aspect in the design of hot water pump rooms. Choosing a too large diameter will increase construction costs, while choosing a too small diameter will raise operational expenses. 2.3.1 Calculation for the selection of the diameter of the hot water pump inlet: Referring to the design specifications for oil and gas transportation, the pump inlet manifold should have favorable suction conditions, with the flow velocity in the inlet manifold generally not exceeding 1.0 m/s. Here, v = 0.9 m/s is taken for a trial calculation. Therefore, the spiral-welded submerged-arc welded pipe D323.9×7.1 was selected; the flow velocity was calculated based on this pipe diameter to be v = 0.96 m/s. The diameter of the pump inlet pipe should be one size smaller than that of the pump inlet manifold; therefore, 20# seamless steel pipe with dimensions D273×7 was used. The resulting flow velocity was v = 0.69 m/s, which meets the requirements specified in the standards. 2.3.2 Calculation for the selection of the diameter of the hot water pump outlet pipe: The flow velocity in the pump’s discharge manifold is generally between 0.8 and 2.0 m/s, and it should not exceed 1.5 m/s. Here, a flow velocity of v = 1.3 m/s is taken for trial calculation. Therefore, 20# seamless steel pipe D273×7 was selected; the flow velocity was calculated based on this pipe diameter to be v = 1.37 m/s. The diameter of the pump outlet pipe should be one size smaller than that of the pump outlet manifold; therefore, 20# seamless steel pipe with dimensions D219×6 is used. The resulting flow velocity is v = 1.07 m/s, which meets the requirements specified in the standards. The final diameters of each pipe are shown in the table below: Table 1: Table of Diameters and Materials for Inlet and Outlet Pipes of Hot Water Pumps. Sequence Number, Name and Specifications, Remarks: 1. Diameter of pump inlet pipe: D273×7, 20# seamless steel pipe; 2. Diameter of pump inlet manifold: D323.9×7.1, spiral-welded submerged arc welded steel pipe L245; 3. Diameter of pump outlet pipe: D219×6, 20# seamless steel pipe; 4. Diameter of pump outlet manifold: D273×7, 20# seamless steel pipe; 5. Diameter of pipe connecting the pump inlet and outlet manifolds: D89×4, 20# seamless steel pipe; 6. Diameter of flow meter tube: D219×6, 20# seamless steel pipe. 2.4 Process and Installation of Hot Water Pump Rooms: When the area of a hot water pump room exceeds 100 m2, there should be no fewer than 2 doors, one of which must be large enough to accommodate the entry and exit of the largest equipment. However, a small pump room with 1 to 2 pumps can be equipped with one door, and the door of the pump room should open outward. The floor of the pump room should be at least 200 mm above the surrounding ground level; it should be made of concrete. The foundation of the pumps should be at a height of no less than 100 mm. A drainage groove should be installed in front of the pump foundation. 2.4.1 Process in the hot water pump room The flow diagram of the hot water pump room is quite simple; see Figure 2. Supplementary cold water, heating return water, oil tank temperature maintenance return water, etc. — Return water tank inlet — Return water tank outlet — Hot water pump inlet manifold — Hot water pump — Hot water pump outlet manifold — Sent to the heater after hot water measurement. Figure 2: Flow diagram of the hot water pump room. 2.4.2 Elevation of the hot water pump inlet pipe and dimensions of the foundation: During installation, the outlet flange of the hot water pump is directly welded to the reducer, and then a short pipe section is connected; attention should be paid to the length of this short section. The pressure gauge is welded to this short section, which is then welded to an elbow; the elbow is directly welded to the pump inlet manifold. The bottom elevation of the inlet manifold for the hot water pump is set at 0.10 m. The inlet elevation of the hot water pump is determined using graphical methods, and the center elevation of the pump’s inlet as well as the elevation of the top of the pump’s foundation are determined by taking into account the elevation of the top of the pump’s foundation (which should be 200 mm above the ground level, with a minimum of 100 mm). The hot water pumps used at Xi Liu Station 10 are of the PAC80-400B model, manufactured by Zhejiang Keler Pump Co., Ltd. The distance from the center of the anchor bolts to the edge of the foundation should be at least 150 mm; therefore, the distances from the bolts on the motor side to the foundation edge are set at 280 mm and 185 mm, while the distances from the anchor bolts on the pump inlet side to the foundation edge are set at 320 mm and 185 mm. Based on the dimensions of the hot water pump, the dimensions of the pump foundation were determined (length × width: 2200mm × 1100mm). 2.4.3 Installation of pipelines and equipment in the hot water pump room (1) Lengthwise installation: This hot water pump room is already built; its dimensions are 11,000 mm × 7,500 mm, which makes the overall installation layout quite challenging. To save space, the clear distance between the hot water pump outlet pipe and the wall is set at 750 mm. The elbow on the outlet pipe is welded directly to the check valve; as a result, the elbow and the check valve together take up 1230 mm in length. It has been determined that the distance from pump #1 to the center line of the wall is 2250 mm. Given that the width of the pump foundation is 1100 mm, and considering that the minimum clearance between pumps should be 750 mm, the distance between the centers of Pump #1 and Pump #2 was set at 2630 mm; the distance between the centers of Pump #2 and Pump #3 is also 2630 mm. Hot water is metered on-site using differential vortex flow meters, which are installed along the right wall at a distance of 500 mm from it. Due to the large diameter of the pipes, in order to minimize the installation height, flanges of different sizes are used on the valve located near the flow meter, which helps to reduce the installation height significantly. (2) Installation in the width direction: Place the hot water pump outlet manifold near the front end of the pump, with the hot water pump inlet manifold and the pump outlet manifold arranged parallel to each other. This arrangement takes into account the width of the room, as well as facilitating the connection between the pump outlet manifold and the return tank outlet. The clear space on the motor side of the hot water pump from the wall should meet the requirements for operation and maintenance of the motor assembly, and should not be less than 1 m; here it is set at 1.5 m. A floor drain groove 150 mm wide is installed 100 mm in front of the pump foundation. The pump inlet manifold and the return pipe of the return water tank are arranged in parallel, with a distance of 300 mm between the pipes. The return water tank extends slightly into the wall, so that the distance from the foundation of the fixed end of the tank to the wall is 810 mm. The inlet and outlet flanges of the tank are directly welded to elbows, and the distance from the inlet and outlet pipes of the tank to the wall is 835 mm; this determines the installation dimensions in the width direction. 2.4.4 Verification of the nominal elevation of the return water tank: The central elevation of the return water tank is calculated based on the elevation of the top of its foundation (usually around 2.00 m). The top elevation of the base of the return water tank must take into account the convenience of operating the tank as well as the suction requirements of the hot water pump. Here, an empirical value of 0.80 m is used to determine the top elevation of the tank’s base, after which the suction conditions for the hot water pump are checked. The length of the pipeline from the return tank outlet to the hot water pump inlet is l = 9.1 m. The fluid is in the mixed friction zone; using the formula, it can be determined that the frictional loss along the suction pipeline of the hot water pump is as follows: while the local hydraulic resistance loss in the suction pipeline is given by… (A simple estimation gives an equivalent pipe length of 78 m). The calculated value for H_suction is ≤, meaning that the pump can operate properly under its installed conditions. When connecting the outlet pipe of the return water tank to the inlet manifold of the hot water pump, it is important to ensure that the elevation of the pipe centers is consistent. The layout of the inlet and outlet pipes of the return water tank, the pipe for supplying cold water, the pipe for returning heating water, and the return pipe of the hot water pump should be arranged in a flexible manner. 2.4.5 Anti-corrosion and insulation of pipelines and return water tanks (1) Anti-corrosion and insulation of pipelines: ① For pipelines without insulation indoors: after rust removal to Sa2.0 level, apply two coats of camphor red anti-rust paint followed by two coats of blended paint. ② Indoor and outdoor insulated pipelines: After rust removal to Sa2.0 level, apply two coats of cresyl red anti-rust paint; insulate them using 50 mm thick self-extinguishing rigid polyurethane foam pipes, and tie them together with D1.2 mm galvanized iron wire (at intervals of 250 mm); cover them with a layer of galvanized iron sheet with a thickness of δ=0.5 mm (galvanized iron sheet is not required for indoor insulated pipelines). (2) Anti-corrosion and insulation inside and outside the container: ① Internal anti-corrosion treatment: After rust removal to Sa2.5 level, apply AFD-02 polyurethane antistatic oil-resistant anti-corrosion coating in two coats on the interior; after drying, the total thickness of the coating should be ≥160–220 μm. ② External anti-corrosion and insulation for the container: After rust removal to Sa2.5 level, apply HC high-chlorinated polyethylene anti-corrosion paint in two coats as a base and two top coats; after drying, the total thickness of the coating should be ≥140μm. Insulation is provided using δ=80mm waterproof composite magnesium silicate boards, with an additional layer of galvanized iron sheet with a thickness of δ=0.5mm applied on top. 3 Conclusion: Due to the high operating pressure of the pipeline, a larger diameter is required. A larger diameter means that the valves take up more space, which in turn makes the pump house that was originally built appear quite cramped and somewhat inconvenient to use. This design also strives to adopt the best and most suitable installation methods, as reflected in the following aspects: (1) Selection of equipment tailored to local conditions, with a compact and aesthetically pleasing layout of the equipment and pipelines. (2) The return water tank is equipped with a built-in level gauge, which facilitates operation; taking into account the requirements for preventing freezing of the level gauge in winter, it is installed indoors. (3) Advanced and reasonable insulation and anti-corrosion measures were adopted to reduce heat loss.