Secondary & Tertiary Heat Recovery
Setting its sights on reducing emissions and possibly some additional governmental edicts to demand them, the company crafts a patent-pending strategy to complement an economizer, focusing on cold makeup water, a deaerator, and a secondary exchanger.
Under the current administration, energy conservation and the environment are taking a greater role than in the past. This may be seen in certain states, too, as regulations regarding emissions and efficiencies are gradually entering the operating standards for boiler rooms.
For example, the State of California recently has circulated its proposed “Best Performance Standards” (BPS) suggesting stringent efficiency standards for fossil fuel-fired boilers, steam generators, and process heaters with firing capacities greater than 5 MMBtuh. There are two BPS options: first is a fully condensing boiler achieving a minimum efficiency of 95% and second, if that’s not attainable, a maximization of efficiency by implementing a heat recovery design based on a maximum approach of 20°F between the stack gas outlet temperature and the process inlet temperature.
Achieving these types of efficiencies requires solutions that may not have been evaluated in the past, especially when natural gas prices were low and returns on investment unacceptably long. Most boiler room operators are well aware of the efficiency gains with traditional boiler economizers. Typical increases in efficiency are 3% to 5%, even on smaller, high-pressure firetube boilers. But where can we squeeze out extra savings? Condensing economizers give a large bang for the buck in heat recovery but they are not economically feasible unless there’s a sufficiently large heat sink, either in makeup or process water. In most cases, this would be roughly equivalent to 50% makeup.
HEAT RECOVERY OPTIONSThere is, however, another type of heat recovery available for those applications in which a lower makeup rate exists (say, 20% to 50%). Called a ThermoCharger (patent pending), this system uses cold makeup water that then cools water from a deaerator through a secondary exchanger before entering a larger (or a secondary) economizer. Gains of two efficiency points or higher may easily be realized this way and the additional expense is small in comparison with the energy recovered. Because the feedwater has been deaerated (and its temperature above the water dewpoint), the materials of construction will be carbon steel.
It is also important to know that by installing secondary and tertiary heat recovery systems NOX and CO2 emissions are lowered. For every one MMBtuh of natural gas saved, more than 100 lb less CO2 will be pumped into our atmosphere, something we can all breathe easier about.
Even if cap and trade legislation is not passed in 2010, there are other state and federal guidelines pending, such as low carbon fuel standards affecting such fuels like domestic ethanol. Because of these possibilities, there is much to be said for reducing energy consumption along with the resultant lowering of emissions. TB