Furnaces – Process – Treating fuel constituent or combustion product
Patent
1986-04-08
1988-05-03
Favors, Edward G.
Furnaces
Process
Treating fuel constituent or combustion product
44620, 110345, F23B 700
Patent
active
047412780
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a carbonaceous solid fuel.
Despite wide-ranging efforts, hitherto it has not proved possible to develop a technically simple and inexpensive process for the removal or reduction of NO.sub.x in the flue gases of coal-burning installations. To remove or reduce NO.sub.x and other undesired components of the flue gases, basically two type of process are used, on the one hand involving the influencing of the combustion cycle, e.g. by the addition of additives to the fuels, and on the other hand the removal of the undesired components from the flue gases themselves. The present invention relates in particular to the reduction of NO.sub.x according to the first-named type of process.
It is known e.g. from GB No. 2046781 to add calcium compounds to carbonaceous solid fuels to reduce the content of undesired components e.g. sulphur compounds in the flue gases.
U.S. Pat. No. 1,990,948 discloses that iron chloride or iron sulphate may be used in the production of solid fuel briquettes.
However, the presence of substantial quantities of chlorine or sulphate in feeds to combustion processes is generally undesirable because corrosion of metallic surfaces may take place, and because the combustion gases will contain harmful materials as a result.
U.S. Pat. No. 3,323,901 discloses the production of pellets containing iron ore, coal, and Portland cement. These pellets are for use as feed to an iron smelting process and therefore will contain substantial quantities of iron ore e.g. 60% by weight. The Portland cement is used as a binder.
There is no suggestion that the presence of iron has any advantageous effect on the level of undesirable components in the gases resulting from combustion. A skilled person reading the disclosure of U.S. Pat. No. 3,233,901 would not be led towards making solid fuels comprising coal, calcium compounds, and quantities of iron compounds less than those which would be present in feeds to iron smelting processes.
U.S. Pat. No. 2,844,112 discloses a method of inhibiting slag formation in boilers fired with residual petroleum by adding various materials to the feed including calcium compounds and iron compounds. However solid carbonaceous materials such as coal behave differently from residual oil fuels as far as slag formation is concerned. Skilled persons would not be led towards adding to coal materials used to inhibit slag formation in residual fuels.
We have now found that a solid fuel with a reduced tendency to form NO.sub.x on combustion can be obtained by using a specific combination of additives.
According to the present invention there is provided a solid carbonaceous fuel containing added calcium compounds characterised in that it contains up to 10% wt, calculated on dry and ash free (daf) solid carbonaceous fuel of calcium oxide or an equivalent quantity of calcium hydroxide, calcium carbonate and/or substances forming these compounds under furnace conditions and also 0.1 to 5% by weight, based on dry ash free (daf) carbonaceous fuel, of added iron added as iron oxide, carbonate, elemental iron or as substantially halogen-free and sulphate-free iron-containing substances forming iron oxide or carbonate under the furnace conditions.
Examples of compounds forming CaO under the furnace conditions are calcium soaps e.g. CaO, Ca(OH), CaCO.sub.3, or as materials containing substantial amounts of them in free form or combined as, eg dolomite CaCO.sub.3.MgCO.sub.3.
The reference to equivalent quantity of other calcium compounds is to be understood as measuring the quantity of the compound providing the same amount of Ca as calcium oxide.
The iron oxide, iron carbonate and/or elemental iron may be fed in substantially pure form. Alternatively they may be fed as iron-rich minerals or industrial waste substances of iron oxide or carbonate, e.g. basic iron hydroxides, waste containing iron from metallurgy, e.g. iron oxide dust, blast furnace dust, blast furnace slurry, LD slurry, roller scale, roller slurry or red mud; iron-rich here means an iron content of at leas
REFERENCES:
patent: 4173454 (1979-11-01), Heins
patent: 4191115 (1980-03-01), Yang et al.
patent: 4302207 (1981-11-01), Paspek
patent: 4388877 (1983-06-01), Molayem et al.
Franke Friedrich H.
Paersch Michael J.
British Petroleum Company p.l.c.
Favors Edward G.
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