Reducing environmental pollution and fouling when burning coal

Abstract

Powder components containing calcium, alumina, silica, iron, magnesium, and a halogen sorbent are used in combination during coal combustion to produce environmental benefits. Sorbents are added to the coal ahead of combustion and / or are added into the flame or downstream of the flame. The alkalinity and chlorine of the powder is minimized in order to mitigate unwanted fouling, especially when used with sub-bituminous and lignite coals.

Description

CROSS REFERENCE TO EARLIER APPLICATIONS[0001]This application claims the benefit of U.S. provisional application Ser. No. 61 / 788,442 filed Mar. 15, 2013, the entire disclosure of which is incorporated by reference.INTRODUCTION[0002]The invention provides compositions and methods for reducing the levels of mercury, nitrogen oxides, and / or sulfur oxides emitted into the atmosphere upon burning of mercury-containing fuels such as coal. In particular, the invention provides for addition of various halogen and other sorbent compositions into the coal burning system during combustion. Use of the sorbents reduces emission of pollutants and prevents fouling in the furnace.[0003]Significant coal resources exist around the world capable of meeting large portions of the world's energy needs into the next two centuries. High sulfur coal is plentiful, but requires remediation steps to prevent excess sulfur from being released into the atmosphere upon combustion. In the United States, low sulfur ...

AI Technical Summary

Benefits of technology

[0002]The invention provides compositions and methods for reducing the levels of mercury, nitrogen oxides, and / or sulfur oxides emitted into the atmosphere upon burning of mercury-containing fuels such as coal. In particular, the invention provides for addition of various halogen and other sorbent compositions into the coal burning system during combustion. Use of the sorbents reduces emission of pollutants and prevents fouling in the furnace.

[0007]Certain coal facility operators qualify for tax credits under §45 of the IRS code for their efforts in reducing emissions of these pollutants. Under certain circumstances, these operators have observed an undesirable fouling in their furnaces. For example, when low sulfur sub-bituminous coals are burned as fuel, deposits tend to form on boiler tube surfaces, which leads to lower heat exchange efficiency and increased costs of operation

[0009]Sorbents for use especially with sub-bituminous and lignite coals are provided that contain low levels of alkali. The high levels of alkali in sorbents of the prior art can contribute to fouling of a furnace in which they are being burned. By reducing the alkalinity of the sorbents, the operator can minimize the sodium and potassium available in the gas phase for unwanted reactions that lead to formation of deposits on boiler surfaces and elsewhere.

[0011]In an aspect, the powder sorbent contains cement kiln dust (CKD), which is helpful in reducing emissions of NOx, with the improvement that, when the CKD is high in alkali, some of the CKD is substituted by lower alkali materials to reach a specification of less than 2% or less than 1% total alkali. In various embodiments, the powder sorbent also meets a low chlorine specification to reduce fouling in sub-bituminous and lignite coals.

Problems solved by technology

But even when coals contain low sulfur, they still contain non-negligible levels of elemental and oxidized mercury and / or other heavy metals.

Unfortunately, mercury is at least partially volatilized upon combustion of coal.

If remediation is not undertaken, the mercury tends to escape from the coal burning facility into the surrounding atmosphere.

However, most mercury is not captured and is therefore released through the exhaust stack.

Mercury is a known environmental hazard and leads to health problems for both humans and non-human animal species.

These contribute to environmental problems such as smog and acid rain.

Under certain circumstances, these operators have observed an undesirable fouling in their furnaces.

For example, when low sulfur sub-bituminous coals are burned as fuel, deposits tend to form on boiler tube surfaces, which leads to lower heat exchange efficiency and increased costs of operation

The high levels of alkali in sorbents of the prior art can contribute to fouling of a furnace in which they are being burned.