US 5,291,841 A · Coal combustion process for SO.sub.x and NO.sub.x control

Abstract

A method of multi-stage combustion of sulfur and nitrogen-bearing coal which provides high combustion efficiency while preventing formation of sulfur- and nitrogen-bearing air pollutants. In the first stage, a major fraction of the hydrocarbons is burned out of the fuel [stage (1a)] at high temperature and the sulfur bound in the coal is freed therefrom and is then captured by reaction with a solid basic compound such as limestone [stage (1b)] at relatively low temperature. In stage 2 the remaining hydrocarbons in the fuel are burned out, and the residual mixture of coal ash and calcium-sulfur compounds is melted, encapsulating the sulfur in the molten slag, and a major portion of the molten compounds is removed from the gas stream. In stage 3, oxidation of CO and H.sub.2 is almost entirely completed and combustion gases are substantially cooled by heat transfer to the working medium. In stage 4, combustion is finally completed in excess air. The entire combustion process is carried out under conditions to prevent formation of oxides of sulfur and nitrogen. In a preferred embodiment oxygen-rich air for combustion is introduced in stages 1a, 2 and 4, and nitrogen-rich air is introduced in stages 1b and 3.

Claims22

Dependent claims

A process for combustion of coal to maximize combustion efficiency while minimizing emissions of the air pollutants SO.sub.x and NO.sub.x, which comprises

introducing pulverized coal and a first oxygen-rich air into a first combustion zone (1a) in a first stage of combustion to form a mixture therein, and subjecting said mixture to combustion in said first combustion zone,
introducing a pulverized solid basic compound capable of reaction with sulfur generated from the coal and a first nitrogen-rich air into the products of combustion from said first combustion zone in a second combustion zone (1b) in said first stage of combustion, to form a mixture therein, and reacting said mixture in said second combustion zone, and forming solid sulfur-bearing compounds,
introducing a second oxygen-rich air into the products of combustion from said first combustion stage in a second stage of combustion (2) to form a mixture therein, and reacting said mixture in said second stage of combustion, to substantially burn out remaining hydrocarbons and to form molten slag, and encapsulating the sulfur-bearing compounds therein, and removing a major portion of said molten slag and said sulfur-bearing compounds from the combustion gas stream, and cooling the combustion gases,
introducing a second nitrogen-rich air into the products of combustion from said second combustion stage in a third stage of combustion (3), and reacting said mixture in said third stage of combustion and cooling the combustion gases, and
introducing a third oxygen-rich air into the products of combustion from said third combustion stage in a fourth stage of combustion (4) and completing combustion and cooling said mixture in said fourth stage of combustion.

2 more elements

A four-stage process for combustion of coal to maximize combustion efficiency while minimizing emissions of toxic air and solid waste pollutants, consisting essentially of

(a) introducing pulverized coal and a first oxygen-rich air into a first combustion zone in a first stage of combustion to form a fluent mixture therein of said coal entrained in said first oxygen-rich air, and reacting said mixture in said first combustion zone in said first stage of combustion and freeing sulfur and nitrogen chemically bound in the coal;
(b) introducing a pulverized solid inorganic alkaline sulfur sorbent and a first nitrogen-rich air into the products of combustion from said first combustion zone in a second combustion zone in said first stage of combustion to form a fluent mixture therein, and reacting said mixture in said second combustion zone in said first stage of combustion and forming sulfur compounds by reaction of sulfur with said alkaline sulfur sorbent;
(c) introducing a second oxygen-rich air into the products of combustion from said first combustion stage in a second stage of combustion to form a fluent mixture therein, and reacting said mixture in said second stage of combustion, melting coal ash and slag, and encapsulating said sulfur compounds in said molten slag, and removing a major fraction of the molten solids from the combustion gas stream;
(d) introducing a second nitrogen-rich air into the products of combustion from said second combustion stage in a third stage of combustion to form a fluent mixture therein, and reacting said mixture in said third stage of combustion and cooling the combustion gases;
and
(e) introducing a third oxygen-rich air into the products of combustion from said third combustion stage in a fourth stage of combustion to form a fluent mixture therein, and completing combustion and cooling said mixture in said fourth stage of combustion to extract the maximum available heat.

3 more elements

A four-stage process for combustion of coal to maximize combustion efficiency while minimizing emissions of toxic air and solid waste pollutants, consisting essentially of

(a) introducing pulverized coal and a first oxygen-rich air into a first combustion zone in a first stage of combustion to form a fluent mixture therein of said coal entrained in said first oxygen-rich air, the oxygen being present in an amount to provide 20-40% of the stoichiometric amount required for complete combustion of said coal, and reacting said mixture in said first combustion zone in said first stage of combustion and freeing sulfur and nitrogen bound in the coal,
(b) introducing a pulverized solid inorganic alkaline sulfur sorbent and a first nitrogen-rich air into the products of combustion from said first combustion zone in a second combustion zone in said first stage of combustion to form a fluent mixture therein, oxygen being present in said first nitrogen-rich air in an amount to provide, together with oxygen from said first combustion zone, about 35-55% of the stoichiometric amount of oxygen required for complete combustion of said coal, and reacting said mixture in said second combustion zone in said first stage of combustion and forming sulfur compounds by reaction of sulfur with said alkaline sulfur sorbent,
(c) introducing a second oxygen-rich air into the products of combustion from said first combustion stage in a second stage of combustion to form a fluent mixture therein, oxygen being present in said second oxygen-rich air in an amount to provide, together with oxygen from said first combustion stage, about 65-85% of the stoichiometric amount of oxygen required for complete combustion of said coal, and reacting said mixture in said second stage of combustion, melting coal ash and slag, encapsulating said sulfur compounds in said molten slag, removing a major fraction of the molten solids from the combustion gas stream, and cooling the second stage combustion gases by more than 400K;
(d) introducing a second nitrogen-rich air into the products of combustion from said second combustion stage in a third stage of combustion to form a fluent mixture therein, oxygen being present in said second nitrogen-rich air in an amount to provide, together with oxygen from said second combustion stage, about 80-100% of the stoichiometric amount of oxygen required for complete combustion of said coal, and reacting said mixture in said third stage of combustion and cooling the combustion gases by more than 300K;
and
(e) introducing a third oxygen-rich air into the products of combustion from said third combustion stage in a fourth stage of combustion to form a fluent mixture therein, oxygen being present in said third oxygen-rich combustion air in an amount to provide, together with oxygen from said third combustion stage, more than 100% of the stoichiometric amount of oxygen required for complete combustion of said coal, and completing combustion and cooling of said mixture in said fourth stage of combustion to extract the maximum available heat.

3 more elements

Dependencies are inferred from the claim text.

Coal combustion process for SO.sub.x and NO.sub.x control

Life of this patent

Coal combustion process for SO.sub.x and NO.sub.x control

Life of this patent

Abstract

Claims22