Steam requirement, consumption

Steam pressure. The main boosters can operate on steam pressures from as low as 0,15 bar up to 7 bar gauge. The quantity of steam required increases rapidly as the steam pressure drops (Fig, 11-106), The best steam rates are obtained with about 7 bar. Above this pressure the change in quantity of steam required is prac tically negligible. Ejectors must be designed for the highest available steam pressure, to take advantage of the lower steam consumption for various steam-inlet pressures. 

Superheated steam may be needed where steam distribution pipework in a plant is over extended distances, resulting in a loss of heat and increase in wetness of the steam. Another case may be where a process requires a temperature above the working pressure of the plant. The third case is where steam is used for turbines. Here it improves the performance of the turbine, where for every 6°C increase in steam temperature it can produce a saving of about 1 per cent reduction in steam consumption. Superheaters may also be supplied as independently fired units. These may be used when either the amount of superheated steam required is much less than the boiler evaporation or is only needed on an intermittent basis. 

A thirty-plate bubble-cap column is to be used to remove n-pentane from a solvent oil by means of steam stripping. The inlet oil contains 6 kmol of n-pentane/100 kmol of pure oil and it is desired to reduce the solute content of 0.1 kmol/100 kmol of solvent. Assuming isothermal operation and an overall plate efficiency of 30 per cent, what is the specific steam consumption, that is kmol of steam required/kmol of solvent oil treated, and the ratio of the specific and minimum steam consumptions. How many plates would be required if this ratio is 2.0 ... 

Economics Typical specific consumption figures (for polymer-grade propylene production) are shown (per metric ton of propylene product, including production of oxygen and all steam required) ... 

A. von Ihering ( Die Geblase ) reports some tests as to steam consumption which indicate from 1.3 to 3.4 lb. of steam required per 1,000 cu. ft. of air handled, the larger sizes being the more economical. 

Energy costs are also lower for the spray dryer MgO process. The higher exit temperature of the flue gas from the spray dryer coupled with the cyclic reheat results in a substantially lower steam requirement. The electrical consumption is 25 lower because of the smaller pumps needed for the S02 absorption area. The diesel fuel cost is lower because of the smaller volume of material disposed of in the landfill. Raw material costs are lower because of the regenerable nature of the spray dryer MgO process. 

The result of systematic assessment of the BASF Ludwigshafen site is shown in Figure 60. The amount of sales products increased by 143 % from 1972 to 1992 however, the factory steam consumption decreased slightly. In 1992, only 33% of the steam requirement was supplied from primary energy. Whereas the fraction of steam produced by combustion of residues remains the same, the largest fraction today is supplied by the utilization of waste heat from chemical plants. Consequently the consumption of primary energy dropped drastically. 

It is a common perception that electrical power consumption is higher with HIGEE compared with the packed column that it replaces. Table 5.1 shows that electrical energy consumption and the steam requirement are less as the solvent rate is lower and the selective absorption of H2S is much higher with the HIGEE than with the packed column. 

The counter-current pattern of adsorption and desorption favors high removal efficiencies. Desorption of the adsorbed solvents starts after the delay required to heat the activated carbon bed. The specific steam consumption increases as the residual load of the activated carbon decreases (Figure 22.1.6). For cost reasons, desorption is not run to completion. The desorption time is optimized to obtain the acceptable residual load with a minimum specific steam consumption. The amount of steam required depends on the interaction forces between the solvent and the activated carbon. The mixture of steam and solvent vapor from the adsorber is condensed in a condenser. If the solvent is immiscible with water the condensate is led to a gravity separator (making use of the density differential) where it is separated into a aqueous and solvent fraction. 

The thermal energy savings depend on the available motive-steam pressure end the compression ratio. From steam-jet performance curves, the ratio of suction vapor to motive steam flow rates is obtained and matched with the total steam requirements for the evaporator. The difference in the low rates between the existing evaporator steam without thermal compression and motive steam is the steam savings. The motive steam rate is the new steam consumption. The... 

Operational costs were calculated by determining electrical power consumption of the pumps, compressors and fans, and the steam required for heating. Table 4 shows the economic potential for all systems. 

Water Consumption and Effluent Characterization. Another advantage of CGCC power generation is derived from lower water requirements. Because more than half of the power generated in a CGCC plant comes from the gas turbine, the water requirement is only 70—80% of that required for a coal-fired power plant, where all of the power is generated from steam turbines. 

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