Page 183 - Boiler plant and distribution system optimization manual

168 Boiler Plant and Distribution System Optimization Manual

Figure 10.63—Steam driven feedwater pump.

Section 10-8 Description
One of the most effective ways to recover en-
Heat Recovery Projects ergy from flue-gas is to use an economizer (Figure
10.19) to heat the feedwater going into the boiler.
At 100 PSIG the temperature of the steam and wa-
CHECkLIST 8 ter in the boiler is about 334°F. The temperature
Heat Recovery Projects approach of the flue gas to steam temperature is
in the range of 50°F to 150°F, depending on firing
1. Install economizers on existing boilers. rate. This can result in a stack temperature from
2. Spray tower heat recovery system 385°F to over 480°F providing a good source for
3. Heat reclaimer heat recovery.
4. Air preheater Hot flue gas contains a lot of wasted energy
5. Heat recovery using plate exchangers and it is very beneficial to put this energy back
6. Waste heat recovery boilers into the boiler with heat recovery equipment. The
7. Blowdown heat recovery rule of thumb for reducing stack temperature is:
8. Use blowdown to keep idle boilers warm for every 40°F the temperature is reduced, a 1%
9. Vent condensers efficiency increase occurs. In this case lowering
10. Waste heat for process applications stack temperature by 200F will result in efficiency
11. Recover steam and heat from high pressure increase of 5%.
condensate recovery systems. Preheating the incoming feedwater also im-
12. Install a condensing economizer to heat proves efficiency. The usual temperature of in-
make-up water. coming feedwater is 212 F to 220 F or higher. This
13. Extract combustion air at the roof level of water can be heated in the economizer improving
the plant. efficiency on the water system side. The Rule of
Thumb for feedwater entering a boiler, is the effi-
ciency goes up by one percent for each 11F rise in
1. ECONOMIzER temperature so, if you can heat the water 220°F to
275°F, will result an efficiency increase of 5%.
Potential Savings
~5%