Boilers
In boilers, economizers are heat exchange devices that heat fluids, usually water, up to but not normally beyond the boiling point of that fluid. Economizers are so named because they can make use of the enthalpy in fluid streams that are hot, but not hot enough to be used in a boiler, thereby recovering more useful enthalpy and improving the boiler's efficiency. They are a device fitted to a boiler which saves energy by using the exhaust gases from the boiler to preheat the cold water used to fill it (the feed water).
Energy heat recovery with condensing economiser.
The boiler room is a huge energy guzzler. It consists of thermal fluid boilers or steam boiler, with exhaust gases through a common chimney. An indirect contact or contact condensing economizer will recover the residual heat from the combustion products. A series of dampers, an efficient control system, as well as a ventilator, allow all or part of the combustion products to pass through the economizer, depending on the demand for make-up water and/or process water. The temperature of the gases can be lowered from 200°C to 10°C, while preheating the process water from 8°C to 80°C. On average over the year, boiler combustion efficiency has risen from 80% to more than 95%. The efficiency of heat produced is directly linked to boiler efficiency. The percentage of excess air and the temperature of the combustion products are two key variables in evaluating this efficiency.
The combustion of natural gas needs a certain quantity of air in order to be complete, so the burners need a flow of excess air in order to operate. Combustion produces water steam and the quantity depends on the amount of natural gas burned. Also, the evaluation of the dew point depends of the excess air. Natural gas has different combustion efficiency curves, linked to the temperature of the gases and the excess air. For example, if the gases are chilled to 38°C and there is 15% excess air, then the efficiency will be 94%. The condensing economiser can thus recover the sensible and latent heat in the steam condensate contained in the flue gases for the process. The economizer is made of an aluminum and stainless steel alloy. The gases pass through the cylinder and the water through the finned tubes. It condenses about 11% of the water contained in the gases.
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