Energy economy Heat exchange

Energy economy can be improved by properly exchanging heat between entering cold streams and leaving warm streams. Ideally, all streams should enter and leave at the same temperature obviously this cannot be achieved. However, heat exchange will permit this goal to be more closely approached. 

As the world crude oil supply dictates, most refiners are cutting crude runs. Too often, one result is an increase in the BTUs required to process a barrel through the crude unit. For the average crude unit, 90% of its energy input is provided by furnaces. Theoretically, both heat exchanger and furnace efficiency increase at lower loads. Why, then, does overall heat economy suffer at lower charge rates A few items that the troubleshooter may ponder are ... 

In many chemical or petrochemical processes, economy dictates that superfluous exotherms be utilized to generate steam as an energy conservation measure. Examples are the cooling of a butane oxidation reaction or the condensation of hot sulfur vapors, steam pressure being generated on the shell side of specially designed heat exchangers. 

Converting Heat to Work. There has been a historic bias in the chemical industry to think of energy use in terms of fuel and steam (qv) systems. A more fundamental approach is to minimise the input of work potential embedded in the fuel and feedstock, as well as work purchased direcdy as electricity. Steam is really just a medium of exchange, like money in an economy. 

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