Operating cost steam

These marginal costing approaches to costing steam are unsatisfactory. Within operating companies, few subjects generate more controversy than the value placed on different steam levels. 

The choice of technology, the associated capital, and operating costs for a chlor—alkaU plant are strongly dependent on local factors. Especially important are local energy and transportation costs, as are environmental constraints. The primary difference ia operating costs between diaphragm, mercury, and membrane cell plants results from variations ia electricity requirements for the three processes (Table 25) so that local energy and steam costs are most important. 

Absence of moving parts and simphcity of construction have frequently justified the use of jets and eductors. However, they are relatively inefficient devices. When air or steam is the motivating fluid, operating costs may be several times the cost of alternative types of fluid-transport equipment. In addition, environmental considerations in todays cnemical plants often inhibit their use. 

For most apphcations, particularly in processing plants, either steam tracing or electric tracing could be used, and the correct choice is dependent on the installed costs and the operating costs of the competing systems. 

Specifications 400 feet of four-inch pipe, 25/hr labor, 0.07/k Vh, 4.00/1,000 steam, 100-foot supply lines. TIC = total installed cost TOC = total operating costs. 

Table 10-62 shows the installed costs and operating costs for 400 feet of four-inch pipe, maintained at four different temperatures, with supply lengths of 100 ft. for both electricity and steam and 25/hr labor. 

Operating costs will include 5 to 10 percent of one worker s time, plus power and fuel required. Yearly maintenance costs will range From 50 to 10 percent of total installed costs. Total power for fans, dr er drive, and feed and prodirct conveyors will be in the range of 0.5 D to 1.0 D". Thermal efficiency of a high-temperature direc t-heat rotary dryer will range from 55 to 75 percent and, with steam-heated air, from 30 to 55 percent. 

Economics Power-recoveiy units have no operating costs in essence, the energy is available free. Furthermore, there is no incremental capital cost for energy supply. Incremental installed energy-system costs for a steam-turbine driver and supply system amount to about 800 per kilowatt, and the incremental cost of an electric-motor driver plus supply system is about 80 per kilowatt. By contrast, even the highest-inlet-pressure, largest-flow power-recoveiy machines will seldom have an equipment cost of more than 140 per kilowatt, and costs frequently are as low as 64 per kilowatt. However, at bare driver costs (not including power supply) of 64 to 140 per kilowatt for the power-recovery driver versus about 30 to 80 per Idlowatt for... 

Elevated Flares See Flares for a general definition. The elevated flare, by the use of steam injection and effective tip design, operates as a smokeless combustion device. Flaring generally is of low luminosity up to about 20 % of maximum flaring load. Steam injection tends to introduce a source of noise to the operation, and a compromise between smoke elimination and noise is usually necessary. When adequately elevated (by means of a stack) this type of flare displays the best dispersion characteristics for malodorous and toxic combustion products. Visual and noise pollution often creates nuisance problems. Capital and operating costs tend to be high, and an appreciable plant area can be rendered unavailable for plant operations and equipment because of excessive radiant heat. 

In the above example, 1 lb of initial steam should evaporate approximately 1 lb of water in each of the effects A, B and C. In practice however, the evaporation per pound of initial steam, even for a fixed number of effects operated in series, varies widely with conditions, and is best predicted by means of a heat balance.This brings us to the term heat economy. The heat economy of such a system must not be confused with the evaporative capacity of one of the effects. If operated with steam at 220 "F in the heating space and 26 in. vacuum in its vapor space, effect A will evaporate as much water (nearly) as all three effects costing nearly three times its much but it will require approximately three times as much steam and cooling water. The capacity of one or more effects in series is directly proportional to the difference between the condensing temperature of the steam supplied, and the temperature of the boiling solution in the last effect, but also to the overall coefficient of heat transfer from steam to solution. If these factors remain constant, the capacity of one effect is the same as a combination of three effects. 

Replacement of the steam-jet ejector with a vacuum pump. The distillation operation will not be affected. The operating cost of the ejector and the vacuum pump are comparable. However, a capital investment of 75,000 is needed to purchase the pump. For a five-year linear depreciation with negligible salvage value, the annualized fixed cost of the pump is I5,000/year. 

In addition to the fixed capital investment needed to purchase and install process equipment and auxiliaries, there is a continuous expenditure referred to as operating cost, which is needed to operate the process. The operating cost (or manufacturing cost or production cost) includes raw materials, mass-separating agents, utilities (fuel, electricity, steam, water, refrigerants, air, etc.), catalysts, additives, labor, and maintenance. The total annualized cost of a process is defined as follows ... 

The centrifugal compressor is well established for the compression of gases and vapors. It has proven its economy and uniqueness in many applications, particularly in which large volumes are handled at medium pressures. This compressor is particularly adaptable to steam turbine or other continuous speed change drives, as the two principles of operation and control are quite compatible. It is also adaptable to the electric motor, gas engine, and gas turbine with each installation being specific to a particular problem or process. Installation as well as operating costs can be quite reasonable. 

Exact performance can be given only by the manufacturer for a specified turbine selected to operate at a particular set of conditions. However, estimates can be made which are usually quite satisfactory for general evaluations and comparisons. The most useful criteria are the steam rate and the system cost. Steam rate is the flow of steam in pounds per brake horsepower output per hour through the turbine. It is established for a definite shaft horsepower output, given steam pressure and temperature, exhaust system pressure, and shaft rpm ... 

An alternative cost also became apparent from the case studies. If the mean hourly steaming rate in kilograms is multiplied by 2.25, it produces a figure roughly equivalent to the annual operating costs in pounds, excluding the cost of fuel. 

Steam traps are installed in condensate, mechanical return systems and are a frequently overlooked item for reducing operating costs. Large industrial process plants typically have many hundreds of steam traps installed to recover low-energy condensate and remove (potentially corrosive) air and carbon dioxide. 

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