The heating coils in the boil and immersion chambers of the degreaser and the
stills are available using steam, direct electric, or hot water. The cooling
requirements are usually supplied by a separate air- or water-cooled chiller
producing chilled water at 50°F for the solvent condenser coils. These require the
addition of energy and the rejection of energy under conventional operation.
By carefully using waste heat recovery, most of this energy can be balanced
out, significantly reducing the net overall energy consumption.
By using a degreaser (and still) with chilled and hot water coils, plus a water-cooled chiller and an industrial heat pump, almost all the energy can be kept within the system. This can significantly reduce operating cost and, in new installations, may even offer a reduced first cost.
By combining a heat pump with the chiller system, the rejected chiller heat can be used to provide the heating load when the heat pump's compressor power is added. In some cases, the chiller rejects more heat than the heat pump can use. A cooling tower or some similar type of heat rejection device would then be needed.
One installation in a metal fabricating and machining facility used a 144- by
60-inch clear work opening vapor degreaser and still. The utility requirements
using the conventional design are:
Heating -- 630,000 Btu/hr heating 42 GPM of water from 130 to 160°F for the
degreaser and still.
Cooling -- 38.5 tons chilling 92.4 GPM of water from 60 to 50F.
In lieu of the conventional design, the plant installed a water-cooled chiller plus a heat pump to supply both the 160°F hot water and the 50°F chilled water. The chiller installed could produce in excess of the required 38.5 tons at 0.76 kW/ton, providing 85°F condenser water as the source heat to the heat pump and producing 50°F chilled water for the degreaser (27.8 tons) and the still (10.7 tons).
The heat pump selected produces 642,000 BTUH of 160°F hot water, with 75°F leaving source water and furnishing 450,000 BTUH of cooling to the chiller with 61.4 kW input power. Since the chiller rejects more heat ((38.5 tons x 12,000 BTUH/ton) + (0.76 kW/ton x 38.5 tons x 3,412)) or 561,000 Btu/hr more than the heat pump requires as source heat, a cooling tower or similar device must be used in the intermediate water loop to reject this surplus heat.
Using the chiller/heat pump system hourly, operating energy consumption is 60.3 kWh for the heat pump plus 29.3 kWh for the chiller for a total of 89.6 kWh. Using conventional design, the hourly energy consumption for a gas-fired hot water heater and air-cooled chiller would be 9 therms and 42 kWh. From this data, an energy cost comparison can be made.
