Архивы рубрики ‘Industrial Boilers and Heat Recovery Steam’

SNCR

In selective noncatalytic reduction a NOx reduction agent such as ammonia or urea is injected into the boiler exhaust gases at a temperature of approximately 1400-1650°F. The ammonia or urea breaks down the NOx in the exhaust gases into water and atmospheric nitrogen, plus CO2 if urea is injected. This reaction takes place in a […]

NOx CONTROL METHODS

Methods for NOx control can be classified into two broad categories: 1. Postcombustion methods: methods that are deployed after flue gases are generated. 2. Combustion control methods: methods that are deployed during the combustion process. Postcombustion Methods As the name implies, postcombustion methods deal with the flue gases obtained after combustion. They are more expensive […]

NOx FORMATION

Nitrogen oxides are of environmental concern because they initiate reactions that result in the formation of ozone and acid rain, which can cause health problems, damage buildings, and reduce visibility. The allowable NOx emissions from boilers and HRSGs vary depending on local regulations but are gradually edging toward single-digit values in parts per million volume […]

HOW POLLUTANTS ARE GENERATED

Before going into further details of how the boiler or HRSG is impacted by emission regulations, one should first understand what the various pollutants are Figure 4.3 Options for NOx removal in boilers and HRSGs. And how they are formed. In the process of combustion of fossil fuels, be it in steam generators, gas turbines, […]

Emission Control in Boilers and HRSGs INTRODUCTION

Boiler and HRSG designs have undergone significant changes during the last few decades with the enforcement of emission regulations in various parts of the world. Decades ago boiler and HRSG users were concerned about two issues only: the initial cost of the boiler or HRSG and the cost of operation. Low boiler efficiency, for example, […]

SPECIFYING PACKAGED BOILERS

The following process data should be specified as a minimum. 1. Steam parameters such as flow, pressure, temperature, and feedwater temperature. If saturated steam is taken from the boiler for deaeration or for NOx control, fuel oil heating, etc., it should be so stated. If the makeup water flow is 100%, the deaeration steam could […]

GLASS EXCHANGERS

Borosilicate glass (Pyrex) tubing has been used in heat recovery applications because it is most resistant to chemical attack and presents no corrosion problems. Fouling is minimal due to the smoothness of the surfaces. These tubes also have a low coefficient of expansion and are resistant to thermal shock, which makes them suitable as heat […]

CONDENSING HEAT EXCHANGERS

The conventional design of economizers and air heaters ensures that cold end corrosion due to condensing sulfuric acid or water vapor does not occur because the minimum tube wall temperature is maintained above the dew points. However, owing to this design philosophy, a significant amount of energy is lost or not recovered in boilers and […]

HEAT PIPES

Heat pipes (Fig. 3.28) were introduced into the heat recovery market about 40 years ago. A heat pipe consists of a bundle of pipes filled with a working fluid such as toluene, naphthalene, or water and sealed. Heat from the flue gas evaporates the working fluid collected in the lower end of the slightly inclined […]

AIR HEATERS

Air heaters are used in a few waste heat boilers for preheating combustion air. Incineration plants and reformer furnaces also use preheated air. Decades ago they were used in boilers that fired solid, liquid, and gaseous fuels. However, with NOx limitations for all kinds of fuels, they are now used only if the combustion of […]


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