The simulation results were then used to size process equipment, develop mass and energy balances, and determine operating conditions and utility consumption of process equipment. Aspen process economic analyzer [25] was used to estimate the equipment purchase costs. The Hand factor was utilized to account for installation and other costs. The fixed capital investment (FCI) for each processing unit was then estimated [26].
(2.1)
where FCIi, fixed capital investment for a given processing unit;
Table 2.4 shows the values and assumptions used to estimate the variable costs (raw material costs were considered separately):
Table 2.4 Parameters used for the techno‐economic analysis.
| Parameter | Values | Units | References |
| Variable cost parameters | |||
| TEG price | 0.93 | $/lb | [27] |
| Refrigerant price | 13.11 | $/GJ | [28] |
| Electricity price | 0.049 | $/kWh | [29] |
| Fuel price | 2.98 | $/MSCF | [30] |
| Plant operator rate | 32.74 | $/h | [31] |
| Plant supervisor rate | 68.13 | $/h | [32] |
| Maintenance | 5 | % of FCI | [25] |
| Operating charges | 25 | % of operating labor cost | [25] |
| Plant overhead | 50 | % of operating labor + maintenance cost | [25] |
| General administrative | 8 | % of all other operating costs | [25] |
| Stream factor | 0.96 | — | — |
The only additional equations used were those to estimate the number of workers based on the number of processing steps [28]:
(2.2)
where Nnp, the number of non‐particulate processing steps, which is related with the number of operators per shift (NOL), given as in Eq. (2.3):
(2.3)
where P, the number of processing steps where particulate solids are handled.
2.4.2.1 Changes in Fixed and Variable Costs
Additional cases were fed through the base case process design, and any needed modifications were made to meet product specifications. Therefore, fixed and variable costs were first estimated as before, and then only the change in each of these costs was used in the subsequent calculations. For fixed costs, the change was only used in cases where the costs were higher, since the need for smaller equipment does not result in any savings for an existing plant.
2.4.2.2 Revenue
Table 2.5 shows the price of each component [33]:
Table 2.5 Price of different commodities.
| Commodity | Units | Base case |
| Heat valuea | $/MMBtu | 2.98 |
| Ethane | $/gal | 0.262 |
| Propane | $/gal | 0.632 |
| n‐Butane | $/gal | 0.691 |
a Methane and wellhead gas are priced in terms of their heat value ($/MMBtu).
2.4.2.3 Economic Calculations
The next step was to calculate the return on investment (ROI) [26]:
(2.4)
where TCI, total capital investment.
First, the quantities in Eqs. must be calculated.
(2.5)
where FCI, total fixed capital investment:
(2.6)
where WCI, working capital investment (assumed to be 15% of FCI):
(2.7)
where AFC, annualized fixed cost (depreciation); FCIS, the salvage value of the FCI (assumed to be 10% of FCI); and N, plant lifetime (assumed to be 10 years):
(2.8)
