Recycling energy cost

Energy cost. The fixed heat loss of 20 X 106 Btu/h can be expressed in terms of methane cost (5.380/lb) using a heating value of 21,520 Btu/lb for methane. The fixed heat loss represents a constant cost that is independent of the variables, hence in optimization we can ignore this factor, but in evaluating the final costs this term must be taken into account. The value for 7 depends on the amount of fuel oil and methane produced in the cracker ( 7 provides for any deficit in products recycled as fuel). 

The DCO oxidant may be electrochemically recycled. If the expended oxidant is not recycled, then the cost of DCO is estimated to be 79.00/kg of carbon destroyed. If the peroxydisulfate is recycled, then the energy cost is 4.00/ kg of carbon destroyed. The total cost of a DCO system using recycled oxidant was estimated to be 10.40/kg of carbon destroyed. These estimates include the cost of oxidant at 0.73/lb, the cost of electricity at 0.06/kWh, labor costs at 120 per day, and capital costs of 100,000. The full-scale unit was estimated to treat 50 kg of carbon per day with an online availability of 80%. The estimates do not include the additional costs of working in a nuclear environment, pretreatment, or stabilization and disposal of the final product (D18455Y, pp. 4, 5 D20886Q, p. 14 D20844G, p. 37 D21204U, p. 2). 

The second item is the concentration of the reactant in the feed. We considered the case in which the feed is pure reactant A and found a heat removal rate for a given conversion and reactor temperature. However, suppose that the feed were a mixture of reactant A and product B. Now for the same feedrate and conversion, there is less of A to react so the heat transfer requirements are lower. This indicates one method of improving reactor controllability, which is to reduce reactant feed composition by diluting the feed with some nonreactive component. Of course, the downside of this approach is that there must be more material to recycle, which increases capital and energy costs. 

The downside of this design is that the excess A must be recovered and recycled, which means high capital and energy costs. However, the resulting improvement in the yield of C is typically well worth the added cost. This is particularly true when the undesirable product D is toxic, corrosive, explosive or an environmental pollutant that is difficult to dispose of. Environmental and safety concerns have pushed the designs of many chemical processes to include several large recycle streams so that the yields of desirable products are increased and the yields of undesirable products are decreased. These recycle streams increase the difficulty of the plantwide control problem. 

Figure 2.62 gives results over a range of reactor volumes. The reactor volume that minimizes TAC ( 1,117,000 per year) is 20 m3, giving a recycle flowrate D of 0.1241 kmol/s. Figure 2.63 gives the values of variables and parameters for the 10 m3 reactor process. The reactor concentration is Ca = 2.099 kmol/m3 (z = 0.262 mole fraction A). The column has 16 trays. The distillate composition is 0.3304 mole fraction A. Energy cost is 427,400 per year. The capital cost of the column is 123,000. The capital cost of the... 

We start by studying the steady-state design and economics of a process with a single adiabatic reactor. The design considers the entire plantwide process reactor, heat exchangers, gas recycle compressor, preheat furnace, condenser, and separator. The economic objective function is total annual cost, which includes annual capital cost (reactor, catalyst, compressor, and heat exchangers) and energy cost (compressor work and furnace fuel). 

---