Energy cost effectiveness

In order to achieve better conversion and selectivity obtained at energy-cost effective method the reaction was selected to be carried out at 250 °C. At this value a conversion of 27.6% with 50% selectivity to CH4 is achieved. 

The use and effective costs of various energy alternatives are shown in Table 2. Use or internal costs include production, transportation, and distribution. Effective costs take into account the use costs estimated external costs, which include costs associated with damage to the environment caused by utili2ation of various fossil fuels and fuel utili2ation efficiencies, ie, the efficiency of converting fuels into mechanical, electrical, or thermal energy. The effective costs are expressed as /GJ of fossil fuel equivalent (15). The overall equation for the effective cost is... 

Fig. 1. Effect of energy use on total cost where total cost is the sum of capital and energy costs for the lifetime of the plant, discounted to present value. Point D corresponds to the design point if the designer uses an energy price that is low by a factor of four in projected energy price. Effects on costs of (a) pressure drop in piping, (b) pressure drop in exchangers, (c) heat loss through insulation, (d) reflux use, and (e) energy recovery through waste-heat boiler...

Because of the low efficiency of steam-ejector vacuum systems, there is a range of vacuum above 13 kPa (100 mm Hg) where mechanical vacuum pumps are usually more economical. The capital cost of the vacuum pump goes up roughly as (suction volume) or (l/P). This means that as pressure falls, the capital cost of the vacuum pump rises more swiftly than the energy cost of the steam ejector, which iacreases as (1 /P). Usually below 1.3 kPa (10 mm Hg), the steam ejector is more cost-effective. 

Other energy considerations for cooling towers include the use of two-speed or variable-speed drives on cooling-tower fans, and proper cooling-water chemistry to prevent fouling in users (see Water, industrial water treatment). Air coolers can be a cost-effective alternative to cooling towers at 50—90°C, just below the level where heat recovery is economical. 

This provides another criterion for testing whether a heat-pump system may be cost-effective. A power plant takes three units of to yield one unit of W. Therefore, to provide any incentive for less overall energy use, Q W must be far in excess of 3. 

The first solar-electric technology to arouse industry interest was solar-thermal energy (1,3,5,6,8). Under favorable circumstances, it can be cost-effective, as evidenced by the fact that solar-thermal gas-hybrid plants produce over 350 MW of commercial power in southern California. This power is used during peak demand to supplement that available from conventional generation. 

Electrodialysis. Electro dialytic membrane process technology is used extensively in Japan to produce granulated—evaporated salt. Filtered seawater is concentrated by membrane electro dialysis and evaporated in multiple-effect evaporators. Seawater can be concentrated to a product brine concentration of 200 g/L at a power consumption of 150 kWh/1 of NaCl (8). Improvements in membrane technology have reduced the power consumption and energy costs so that a high value-added product such as table salt can be produced economically by electro dialysis. However, industrial-grade salt produced in this manner caimot compete economically with the large quantities of low cost solar salt imported into Japan from Austraha and Mexico. 

The issues of faciUtating options such as energy storage and transmission may prove to be important to the success of wind energy technology. Cost-effective storage coupled to wind systems would yield capacity credit benefits. In addition, because sites are often isolated, the value of wind energy would benefit from transmission/distribution access. 

As energy costs have escalated in recent years, the use of high moisture food by-products in commercial animal feeds has also escalated, particularly in beef cattie and dairy rations, as a means of reducing production costs. Because of the broad activity spectmm, sorbates are extremely effective in the preservation of wet by-products, eg, brewers and distillers grains, beet pulp, citms pulp, and condensed whey (139). 

Iron—Air Cells. The iron—air system is a potentially low cost, high energy system being considered mainly for mobile appHcations. The iron electrode, similar to that employed in the nickel—iron cell, exhibits long life and therefore this system could be more cost effective than the ziac-air cell. Reactions iaclude ... 

A topical aspect of differential inflation is the question of energy costs. Will the cost of a particular fuel rise or fall in relation to prices in general, and if so, what effect will this have on the economics of a project ... 

---