OPEX for UV AOP model

[AbbyHodson]

Hello!

I am attempting model two different UV AOPs, one with high CAPEX and low electricity demand (reactor A), and another with low CAPEX and high electricity demand (reactor B). Interestingly, reactor A has a higher OPEX despite lower electricity demand. After some digging, I suspect that the reason for this is that the total_fixed_operating_cost is the sum of aggregate_fixed_operating_cost and maintenance_labor_chemical_operating_cost (which is a function of aggregate_capital_cost) in watertap_costing_package.py. Because the CAPEX is much higher for reactor A than for reactor B, the aggregate_capital_cost and, therefore, OPEX is also higher.

Would anyone be willing to explain to me why OPEX is inherently linked to CAPEX through the maintenance_labor_chemical_operating_cost variable? The major advantage of reactor A should be lower electricity demand and OPEX, but this doesn't come through in my results with the way that OPEX is calculated.

Any advice and insight from more experienced users would be very appreciated!!

[kurbansitterley]

Hi @AbbyHodson - sometimes when doing TEA it is common to link an operating cost to the capital cost via factors if it is a cost we want to capture (in this case the annual cost of maintenance, labor, and chemicals) but don't have a solid relationship for.

The default value for the maintenance_labor_chemical_factor is 0.03 but there is nothing wrong with setting it to zero to exclude these costs (m.fs.costing.maintenance_labor_chemical_factor.fix(0)) in both flowsheets.

Alternatively, you could make your comparison with total_variable_operating_cost which does not include the maintenance_labor_chemical_operating_cost or just the electricity cost with aggregate_flow_costs['electricity'].

[AbbyHodson]

Hmm that makes sense, thank you!