TM-5-855-4
(2) In industrial facilities where process steam is required, medium or high pressure steam
boilers are recommended. Electrically-heated steam boilers are well suited for hardened facilities
having a large demand for humidification steam in the wintertime.
b. As a rule, where diesel-engine jacket water waste heat is recovered in conjunction with waste heat
recovery from the exhaust gases, a hot water boiler is the logical choice. It is estimated that heat recovery
mufflers on the exhaust stack and jacket water heat exchangers can recover 20 to 30 percent of the input
fuel energy which is rejected in exhaust gasses and jacket water. The recovered energy can be
transferred to a hot water or low pressure steam system to heat domestic hot water and the facility. The
quantity of low pressure steam powered by flash vaporization of the jacket water is equal to the heat
recovered divided by the difference between the steam enthalpy and the enthalpy of the feedwater returned
to the flash tank.
c. The combustion gas exhaust temperature must be kept above its acid dewpoint to prevent corrosion
of surfaces in contact with it. Unless the fuel contains no sulfur, a 300 0 F acid dewpoint is usually
assumed. Diesel engine jacket water design will not exceed 2500 F, 45 psi, and 150 F temperature rise to
minimize thermal stresses on the engine. To avoid leaks and over pressure, the primary circulation
loop of the jacket water will be limited to local heat exchangers to transfer the salvaged heat to separate
secondary heating circuits. Another 5 percent of the total fuel input energy may be recovered from the
lube oil system, but at lower temperature levels than the water jacket since the lube oil operating
temperature cannot presently exceed 200 0 F while maintaining reasonable lube oil life.
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