Heat Requirement

British thermal unit (Btu) The most commonly used industrial heal unit the amount of heat required to raise 1 lb of water through UF under specified conditions. Since the specific heat of water varies, particularly with temperature, the actual value of Btu is dependent on the conditions chosen as stan-... 

Where the distance to the customer is very large, or where a gas pipeline would have to cross too many countries, gas may be shipped as a liquid. Gas has to be chilled to -160°C in a LNG plant to keep it in liquid form, and is shipped in refrigerated tankers. To condition the gas for liquefaction any COj, HjS, water and heavier hydrocarbons must be removed, by the methods already discussed. The choice of how much propane and butane to leave in the LNG depends upon the heating requirements negotiated with the customer. 

We have seen that in a metal the atoms are close-packed, i.e. each metal atom is surrounded by a large number of similar atoms (often 12, or 8). The heat required to break up 1 mole of a metal into its constituent atoms is the heat of atomisation or heat of sublimation. Values of this enthalpy vary between about 80 and 800 kJ. for metals in their standard states these values indicate that the bonds between metal atoms can vary from weak to very strong. There is a rough proportionality between the m.p. of a metal and its heat of atomisation. so that the m.p. gives an approximate measure of bond strength. 

The treatment of heat capacity in physical chemistry provides an excellent and familiar example of the relationship between pure and statistical thermodynamics. Heat capacity is defined experimentally and is measured by determining the heat required to change the temperature of a sample in, say,... 

In this condenser, part of the stripper off-gases are condensed (the heat of condensation is used to generate low pressure steam). The carbamate formed and noncondensed NH and CO2 are put into the reactor bottom and conversion of the carbamate into urea takes place. The reactor is sized to allow enough residence time for the reaction to approach equiUbrium. The heat required for the urea reaction and for heating the solution is suppHed by additional condensation of NH and CO2. The reactor which is lined with 316 L stainless steel, contains sieve trays to provide good contact between the gas and Hquid phases and to prevent back-mixing. The stripper tubes are 25-22-2 stainless steel. Some strippers are still in service after almost 30 years of operation. 

Product temperature below space temperature (producing a credit to sensible-heat gain or a heating requirement)... 

Salt that is substantially free of sulfate and other impurities is the cell feed. This grade may be purchased from commercial salt suppHers or made on site by purification of cmde sea or rock salt. Dried calcium chloride or cell bath from dismanded cells is added to the bath periodically as needed to replenish calcium coproduced with the sodium. The heat required to maintain the bath ia the molten condition is suppHed by the electrolysis current. Other electrolyte compositions have been proposed ia which part or all of the calcium chloride is replaced by other salts (61—64). Such baths offer improved current efficiencies and production of cmde sodium containing relatively Htde calcium. 

Spent acid burning is actually a misnomer, for such acids are decomposed to SO2 and H2O at high temperatures in an endothermic reaction. Excess water in the acid is also vaporized. Acid decomposition and water vaporization require considerable heat. Any organic compounds present in the spent acid oxidize to produce some of the required heat. To supply the additional heat required, auxiUary fuels, eg, oil or gas, must be burned. When available, sulfur and H2S are excellent auxiUary fuels. 

Overall comparison between amine and carbonate at elevated pressures shows that the amine usually removes carbon dioxide to a lower concentration at a lower capital cost but requires more maintenance and heat. The impact of the higher heat requirement depends on the individual situation. In many appHcations, heat used for regeneration is from low temperature process gas, suitable only for boiler feed water heating or low pressure steam generation, and it may not be usefiil in the overall plant heat balance. 

If FCCU operations are not changed to accommodate changes ia feed or catalyst quaUty, then the amount of heat required to satisfy the heat balance essentially does not change. Thus the amount of coke burned ia the regenerator expressed as a percent of feed does not change. The consistency of the coke yield, arising from its dependence on the FCCU heat balance, has been classified as the second law of catalytic cracking (7). 

The theoretical energy requirement for the burning of Portiand cement clinker can be calculated from the heat requirements and energy recovery from the various stages of the process. Knowledge of the specific heats of the various phases, and the heats of decomposition, transformation, and reaction then permits calculation of the net theoretical energy requirement of 1760 kj (420 kcal) for 1 kg of clinker from 1.55 kg of dry CaCO and kaolin (see Clays) (8). 

In a study on dewatering methods for peat, displacement dewatering was done using acetone, a polar solvent having a lower heat of vapori2ation than water. Dewatering was improved in terms of both the pressure filtering step and the quantity of heat required. Less heat was required to dry the cake and recover the acetone from the filtrate by distillation (31). 

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