Abstract: A process and apparatus are described which enable urea plant process condensate, which is contaminated with urea and other combined forms of ammonia and carbon dioxide, to be converted substantially completely and on a continuous basis, to a gaseous stream comprising steam, ammonia, carbon dioxide and hydrocarbon gas (introduced in the processing of the condensate). The gaseous stream so recovered is employed as feedstock for use in the reformer of the ammonia plant which supplies ammonia and carbon dioxide feedstocks for the synthetic urea plant from which the treated process condensate was derived. In a preferred embodiment the hydrocarbon fuel gas is natural gas. The process of the invention obviates the environmental and like problems hitherto encountered in the handling of urea plant process condensate and also provides marked advantages including improving the economics of operation of the urea plant and associated ammonia reformer plant.

Abstract: A system for recovering heat from combustion flue gas, which transfers heat from the flue gas into combustion-supporting air, which is then used to burn a fuel in a combustion zone in a furnace or the like, so that useful heat is generated and a hot combustion flue gas is formed. Two heat sinks are provided, each for alternate absorption of heat from the hot flue gas, and desorption of heat into ambient combustion air so that the air is preheated. A reversible fan or blower is associated with each sink. The hot flue gas is passed successively through one heat sink and fan to atmospheric discharge for a finite time interval, while concomitantly passing cold and usually ambient combustion air successively through the other fan and heat sink so that the air is heated and a preheated combustion air stream is formed, which is subsequently passed to the combustion zone. After the finite time interval, the reversible fans are reversed for another finite time interval usually equal to the first time interval.