The meters and dehydrators were priced as installed units. The wells, gathering system, and the transmission also were priced from the design using the economic factors in Table 7-5. No attempt was made to block out the compressor horsepower into commercially available units. The investment in compressors is broken down into the operating units and the spare unit. For the cases of 600, 800, and 1,000 psia the injection compressor horsepowers govern. For the cases of flowing wellhead pressures of 200 and 400 psia the withdrawal compressor horsepowers govern. The investment costs are calculated using the economic factors in Table 7-5. In Table 7-7 the installed horsepower includes 33 percent spare capacity. If the sizing is such that three units are required, four are purchased. Quite often a single spare compressor is purchased. The amount of this spare horsepower will depend on the operating philosophy of the individual company. In addition, some spare horsepower is required. This usually results in an increase above the minimum required. The available sizes must be tailored to the needs.
Since horsepower comes in size blocks, it is not always possible to purchase the minimum horsepower required.
#Tabular view manual
The computer model (or a manual calculation) will determine the minimum required horsepower. It should be noted that there is a shift in the governing cycle as the pressure changes. The cycle that requires the most horsepower will then govern. This simulation should be made for both the injection cycle and the withdrawal cycle. This computer model will then calculate the pressures at the various points in the system and also calculate the required horsepower. The entire facility should be simulated by a computer model.
This variation in size will be due to the variation in withdrawal rates. The only variation from case to case should be in the size of the transmission line and in the size of some of the trunk lines in the gathering system. The gathering system and the transmission line should be designed for each of these cases.
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