Environmental Engineering Reference
In-Depth Information
Automatic adjustment of air-to-fuel ratio requires energy-efficient burners capable of
adjusting precisely the quantities of fuel according to the load and the corresponding amount
of air. These burners maximize combustion efficiency and reduce the amount of excess air
needed for combustion (DOE, 2006c).
Minimize heat loss in blowdown water
Boiler blowdown is a necessary practice to maintain the water solids content at acceptable
limits. No matter how efficient the feed water treatment is, water always contains a certain
degree of impurities that accumulate inside the boiler as a result of water evaporation.
Concentration of impurities are maintained at acceptable levels by purging water from the
boiler at regular intervals, which is know as “blowdown.” Solids accumulate either at the
water surface or at the bottom of the boiler (sludge). Surface solids are removed by surface
blowdown, which is often a continuous process, and sludge is removed by mud or bottom
blowdown (DOE, 2006d).
The negative aspect of blowing down water, which has the same temperature as the steam
the boiler is producing, is energy loss. This can be minimized by installing an automatic con-
trol system that continuously monitors the water conductivity and actuates valve that releases
controlled volumes of water to keep the conductivity to a certain level.
A second approach to minimize energy loss to blowdown water is the installation of a heat
recovery system. There are several configurations, but the most common is the discharge of
the hot water into a flash tank, where water is transformed in low-pressure steam that feeds a
heat exchanger used to heat makeup water.
Improve insulation
The US Department of Energy (DOE) recommends insulating any surface with temperatures
above 49°C (120°F) to minimize heat loss. This includes boiler surfaces, steam distribution
lines, condensate return pipes, valves, and fittings (DOE, 2006e).
Return condensate to boilers
When steam condenses in a heat exchanger or similar device, it releases its latent energy dur-
ing the phase change. The condensate still retains important amounts of sensible energy; and
therefore collecting and returning the condensate to the boiler improves the efficiency of the
whole system. Moreover, condensates are made of high purity water that when returned to the
boiler reduces the amount of external makeup water needed. This not only reduces the amount
of energy to heat makeup water, but it also results in a reduction of chemicals consumption, a
cut in blowdown volumes, and a reduction in the volume of wastewater.
Fix steam leaks
Steam leaks are common in older processing facilities, which happen as a result of faulty
threaded pipe connections, valve stem packing, pressure relief valves, and poorly seated valves.
Even when the volume of steam lost to leaks is difficult to quantify, in the long run, constant
steam leaks result in wasted energy and money that can be avoided by just fixing the problem.
The following four subsections deal with efficiency improvement of processes that are
subjected to direct heating.
Recover heat from processes
The section titled, “Heat Recovery” details this process.
Use proper heating methods
See section on improving boiler efficiency.
