Cooling Costs

Once the minimum utility cost has been identified, tradeoffs between operating and fixed costs must be established. This step is undertaken iteratively. For given values of minimum approach temperatures, the pinch diagram is used to obtain minimum cooling cost and outlet gas temperature. By ccmducting enthalpy balance around each unit, intermediate temperatures and exchanger sizing can be determined. Hence, one can evaluate the fixed cost of the system. Next, the minimum approach temperatures are altered, until the minimum TAC is identified. 

The reason for this is simple. If the reaction chemistry is not "clean" (meaning selective), then the desired species must be separated from the matrix of products that are formed and that is costly. In fact the major cost in most chemical operations is the cost of separating the raw product mixture in a way that provides the desired product at requisite purity. The cost of this step scales with the complexity of the "un-mixing" process and the amount of energy that must be added to make this happen. For example, the heating and cooling costs that go with distillation are high and are to be minimized wherever possible. The complexity of the separation is a function of the number and type of species in the product stream, which is a direct result of what happened within the reactor. Thus the separations are costly and they depend upon the reaction chemistry and how it proceeds in the reactor. All of the complexity is summarized in the kinetics. 

To maintain the target level for temperature, a specific amount of insulation may be needed, since too little insulation makes it impossible to keep the temperature levels. For each building it is necessary to make a detailed cost-benefit calculation of insulation and heating/cooling costs. The same discussion is applicable to temperature variation requirements, both for the rate of change and the period lengths (see Chapter 16). 

Although from theoretical considerations biomass yields from methane could be as high as 1.4, in laboratory-scale cultures values of about 1.0 were obtained, and in larger scale systems values were around 0.3-0.6. Methane fermentation also incurs high aeration and cooling costs. 

Use Scalable Heat Transfer. The feed flow rate scales as S and a cold feed stream removes heat from the reaction in direct proportion to the flow rate. If the energy needed to heat the feed from to Tout can absorb the reaction exotherm, the heat balance for the reactor can be scaled indefinitely. Cooling costs may be an issue, but there are large-volume industrial processes that have Tin —40°C and Tout 200°C. Obviously, cold feed to a PFR will not work since the reaction will not start at low temperatures. Injection of cold reactants at intermediate points along the reactor is a possibility. In the limiting case of many injections, this will degrade reactor performance toward that of a CSTR. See Section 3.3 on transpired-wall reactors. 

TABLE 27. Operation cooling cost from the Sundsvall Regional Hospital snow cooling plant (Larsson, 2005)... 

Larsson (2005) predicts that the operation cooling cost in 2004/2005 will be 0.85 SEKkWh-1, andabout0.50 SEKkWh-1 in2010. Thanks to the commitment of CCV, occurring problems have been solved, necessary reconstructions have been made and the plant has worked satisfactorily. 

The objective function. The main costs of operation are the heating and cooling costs that are related to Ql and Qn, respectively. We assume all the other values of Qk are zero. Qn is determined from the energy balance, so that Qx is the independent variable. The cost of operation per annum is assumed to be directly proportional to Qx because the maintenance and cooling costs are relatively small and the capital costs per annum are already fixed. Consequently, the objective function is relatively simple ... 

Controlling Quality of Two Products Where the two products have similar values, or where heating and cooling costs are comparable to product losses, the compositions of both products should be controlled. This introduces the possibility of strong interaction between the two composition loops, as they tend to have similar speeds of response. Interaction in most columns can be minimized by controlling distillate composition with reflux ratio and bottom composition with boil-up, or preferably boil-up/bottom flow ratio. These loops are insensitive to variations in feed rate, eliminating the need for feedforward control, and they also reject heat balance upsets quite effectively. 

Cast Water Cooled MGO 6S0 F 35 Efficient cooling Cost, Water leaks. Scaling... 

Decrease in cooling costs - (Cooling load decrease)(Unit cost of electricity)/COP = (10,262 kWh/year)( 0.08/k Vh)/2.5 = 328/year... 

Cost. savings = Decrease in cooling costs - Increase in healing costs = 328 - 236 92/y ar... 

Oxidation of n-alkanes is stroi y exothermic, the production of 1 kg biomass liberating 27,100 k Joules. Cooling costs to maintain temperatures at about 30°C are considerable. 

The rate of profit is the rate of increase in the value of the process stream less the reactor and cooling costs. Find the value of F that maximizes the profit and the corresponding maximum profit and volume of the reactor. Explain how you would check that this is truly a maximum. 

Any excess electricity along with cogenerated heat is used by the bank and results in the lower life-cycle cost. Also, the fuel cell does not require an air-conditioned area like traditional UPS systems. This results in almost 30,000 saved in annual cooling costs. The system results in more than 40% lower emissions of C02 and less than 1 /1,000 the emissions of other air pollutants. 

Temperature is a particularly important variable in industrial combustion applications because it directly or indirectly affects a number of other important variables. The product temperature is often a critical parameter in most processes. While there is usually a minimum temperature that must be reached for adequate processing, there may also be a maximum temperature above which product quality is reduced. Higher than necessary product temperatures not only increase fuel costs, but they may also increase cooling costs after the product exits the combustion process. Temperature affects the heat transfer in a furnace [1]. Thermal NOx emissions are exponentially dependent on flame temperatures [2]. Combustion chemistry is very complicated and dependent on temperature. High exhaust gas temperatures mean reduced thermal efficiency [3]. 

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