Table 82 Wasteheat sources in the mediumtemperature range

Type of Device

Temperature (°F)

Steam boiler exhausts 450-900

Gas turbine exhausts 700-1000

Reciprocating engine exhausts 600-1100

Reciprocating engine exhausts 450-700 (turbocharged)

Heat treating furnaces 800-1200

Drying and baking ovens 450-1100

Catalytic crackers 800-1200

Annealing furnace cooling systems 800-1200 Selective catalytic reduction systems for NOx control 525-750

utilized to preheat combustion air or boiler make-up water, respectively. At the lower end of the range heat pumps may be required to raise the source temperature to one that is above the load temperature. An example of an application which need not involve heat pump assistance would be the use of 95°F cooling water from an air compressor to preheat domestic hot water from its ground temperature of 50°F to some intermediate temperature less than 95°F. Electric, gas-fired, or steam heaters could then be utilized to heat the water to the temperature desired. Another application could be the use of 90°F cooling water from a battery of spot welders to preheat the ventilating air for winter space heating. Since machinery cooling can't be interrupted or diminished, the waste-heat recovery system, in this latter case, must be designed to be bypassed or supplemented when seasonal load requirements disappear. Table 8.3 lists some waste-heat sources in the low-temperature range.

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