Steam requirements, minimum

The plant is designed with an excellent heat-exchange system to kee overall steam required to a minimum. 

UK. = Light key component in volatile mixture L/V = Internal reflux ratio L/D = Actual external reflux ratio (L/D) ,in = Minimum external reflux ratio M = Molecular weight of compound Mg = Total mols steam required m = Number of sidestreams above feed, n N = Number of theoretical trays in distillation tower (not including reboiler) at operating finite reflux. For partial condenser system N includes condenser or number theoretical trays or transfer units for a packed tower (VOC calculations) Nb = Number of trays from tray, m, to bottom tray, but not including still or reboiler Nrain = Minimum number of theoretical trays in distillation tower (not including reboiler) at total or infinite reflux. For partial condenser system,... 

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 ... 

The primary characteristic of an acid/base buffer affecting steam requirements is the temperature dependence of Pgc /P O-Since PSC /P O of the citrate system is independent of temperature, the ideal minimum steam requirement (moles H20/moles SO2) of a simple stripper is equal to the ratio, °f the... 

Table IV gives minimum steam requirement (infinite stages) at several different solution capacities. The factor attribu-able to equilibrium nonlinearity increases as more SO2 is absorbed, because the buffer capacity is consumed to a greater extent. Any capacity for SO2 absorption can be achieved by varying Na concentration (pH) in the solution. At low pH ([Na] = 1.5 M) the solution capacity for SO2 absorption is small, but the nonlinearity factor is also small (1.05). Solution capacity can be increased by operating at higher pH ([Na] = 2.5 M), but nonlinearity is more severe (1.32).

As shown by case 3 in Table IV, the minimum steam requirement in an optimized system is not sensitive to the magnitude of PSO2 °ver the solution, but only to its dependence on temperature... 

Figure 7. Minimum steam requirement, simple absorption/stripping with live steam, 3000 ppm SOg in at 55°C, 90% removal, I.OM. citrate, 2.0M Na...

Losses of nitric acid and magnesium salts are trivial, and the process can be run in a straightforward manner with minimum manning. The major operational cost is for the steam required for the process heat supply this depends on the concentration range required but will be ca. 2.0—2.5 parts per part of product acid. The capital cost of a commercial plant compares favorably with that for alternative concentration processes. 

The thermal integration of the system has a significant impact on the fuel conversion efficiency of the hydrogen production system. An optimal process configuration that generates the process steam with minimum parasitic losses was selected, and the fuel conversion efficiency on an LHV basis was estimated to be 75.2%. Compressor calculations showed that electricity required was around 1% of the LHV of the fuel. 

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. 

Once interstage pressures have been estimated, the steam requirements for each stage can be also estimated from Figure 23-17. If the estimates indicate steam flows less than 50 Ib/hr, the design air load should be adjusted so that 50 Ib/hr of steam is required as the minimum to any stage. Normally, the atmospheric pressure discharge stage will have a suction pressure of about 150-200 torr and will require the least amount of steam. 

Other significant water uses are boiler water and process water. Boiler water, almost totally evaporated in the boiler to make steam, requires more intensive treatment than cooling water. As a minimum, all of the hardness ions (e.g., calcium and magnesium ions) will be removed. It is common for treatments to remove virtually all dissolved salts from water to be used in boilers, especially high-pressure boilers. 

Reagent Dilution/Cairier Gas Requirements Diluted with water to 5-25% concentration. Air is the carrier gas. (Steam is no longer used.) Typically, 4 scfm of plant air per injector is currently used for atomization and for injector cooling. Not diluted with water. Air or steam at 1-2% of the flue gas flow rate is the carrier gas. This gas requirement is reduced by the amount of water vaporized if aqueous ammonia is vaporized. Not diluted with water. Carrier gas is air, flue gas, or possibly steam at about 2 psig. Ammonia/carrier gas volumetric ratio is a minimum of about 1 to 20 for anhydrous ammonia to keep the ammonia concentration in the air below the lower explosive limit. Lower concenuations may be used based on injection diffusion patterns, the ammonia vaporization heat requirement, minimum flow control ranges, and other factors. 

The highly exothermic nature of the butane-to-maleic anhydride reaction and the principal by-product reactions require substantial heat removal from the reactor. Thus the reaction is carried out in what is effectively a large multitubular heat exchanger which circulates a mixture of 53% potassium nitrate [7757-79-1/, KNO 40% sodium nitrite [7632-00-0], NaN02 and 7% sodium nitrate [7631-99-4], NaNO. Reaction tube diameters are kept at a minimum 25—30 mm in outside diameter to faciUtate heat removal. Reactor tube lengths are between 3 and 6 meters. The exothermic heat of reaction is removed from the salt mixture by the production of steam in an external salt cooler. Reactor temperatures are in the range of 390 to 430°C. Despite the rapid circulation of salt on the shell side of the reactor, catalyst temperatures can be 40 to 60°C higher than the salt temperature. The butane to maleic anhydride reaction typically reaches its maximum efficiency (maximum yield) at about 85% butane conversion. Reported molar yields are typically 50 to 60%. 

Carbon produced by these latter reactions is formed in the catalyst pores, making it much more difficult to remove, and potentially causing physical breakage. Operating steam to carbon ratios are chosen above the minimum required in order to make carbon formation by these reactions thermodynamically impossible (3). Steam is another potential source of contaminants. Chemicals from the boiler feedwater or the cooling system are poisons to the reformer catalyst, so steam quality must be carefully monitored. 

The ignition temperature is the minimum temperature required to initiate or cause self-sustained combustion. Table 2 also Hsts ignition temperatures of several common ethers. Attention is directed to the particularly low ignition temperature of ethyl ether, especially with reference to some common ignition sources such as a lighted cigarette (732°C) or a pressurized (0.7 MPa or 100 psi) steam line (180°C). 

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