Energy Conservation in Boiler House by Using Variable Speed Control

摘要

Boilers should always be supplied with more combustion air than theoretically required in order to ensure complete combustion and safe operation. At the same time, boiler efficiency is very dependent on the excess air rate. Therefore, the excess air should be optimized to increase the system efficiency. In this study, the effect of the excess air ratio on the efficiency of the boiler system was investigated in a water tube boiler that has the capacity of producing 20 bar pressure and 55 ton steam at 245℃. The boiler combustion air is supplied from a fan driven by a 30kW at 1450 rpm induction motor. Since the fan motor, running at nominal speed, has supplied the same air flow rate, excess air amount and exhaust gas temperature were very high at low loads. In that stage, boiler efficiency was low due to thermal energy losses, which also consequently leads to electrical energy losses. The steam requirement of the factory changes because of the tire process. For example, in the tire cooking machines, steam and hot water are not required during the changing of tire castings. In order to increase the boiler efficiency, the fan motor speed is decreased to 400 rpm from 1450 rpm by using variable speed controller. After implementation of variable frequency drive (VFD), stack temperature was reduced from 195℃ to 145℃. This caused an increase of boiler efficiency of 2.5 percent, and 10,000 kW electrical energy was saved in a month. In this article, the energy losses associated with excess air rate and their cost to the manufacturer are evaluated and quantified. An overview of such conservation measures, complete with the analysis, potential energy and cost saving, implementation cost, and simple payback periods are also given.