Drying and gas or vapor contact with solids – Apparatus – With means to treat gas or vapor
Patent
1991-10-29
1993-03-09
Bennet, Henry A.
Drying and gas or vapor contact with solids
Apparatus
With means to treat gas or vapor
34 30, 34 60, 34 54, 34 29, F23K 100
Patent
active
051917246
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of adjusting the operation of apparatus for grinding a solid fuel material having a variable moisture content, and for drying said material, said apparatus being fed with material via pre-drying means in which there is a gas feed whose temperature can be adjusted over a range, the feed gas being split into two fractions, one fraction of the gas passing through the grinding apparatus and the other fraction of the gas being sent to the pre-drying means, the flow rate Q.sub.1 of the fraction of the gas passing through the apparatus being adjusted to be proportional to the flow rate Q.sub.c of material to be ground, the fraction of gas passing through the pre-drying means rejoining the fraction of gas leaving the apparatus together with the ground material, and all of the gas and ground material being sent via conveyor pipework, the temperature T of the gas and the ground material in said conveyor pipework being measured, the temperature of the feed gas being adjusted as a function of the difference between a set temperature T.sub.1 and the measured temperature T in such a manner as to cause the measured temperature T to move closer to T.sub.1, the flow rate Q.sub.2 of the gas fraction feeding the pre-drying means being adjusted in such a manner that the total gas flow rate Q.sub.A in the conveyor pipework lines between a minimum flow rate Q.sub.Am and a maximum flow rate Q.sub.AM.
Such a method is described in an article by Vergniol published in the French journal "Revue Alsthom" No. 1, 1985, pp. 31 to 40, and entitled (in translation) "A single grinder per direct heating boiler".
In the prior method, adjustment is provided for a fuel material having the highest degree of moisture that can normally be used in the boiler under consideration.
The flow rate through the outlet pipework must be not less than a minimum flow rate since below that rate the ground material is no longer transported properly. Also, this flow rate cannot exceed a maximum flow rate since above that rate the ducting is damaged by erosion.
As a result, for an entire range of fuel material having lower moisture content than the material for which the boiler is adjusted, in order to obtain the desired outlet temperature it is necessary to add much too much gas in the pre-drying means and also to reduce the temperature of the feed gas, thereby giving rise to poor efficiency.
In addition, when increasing the quantity of ground material to the maximum possible, the inventor has observed that it is advantageous for the flow rate Q.sub.2 of the pre-drying gas fraction to be adjusted as low as possible so that the total gas flow rate Q.sub.A through the conveying pipework is equal to or very slightly greater than the minimum flow rate Q.sub.Am for as long as possible, and then diverges therefrom, if necessary, by the smallest possible amount.
The resulting efficiency is also increased, and in addition combustion takes place with reduced formation of nitrogen oxides.
The method of the invention is characterized in that a temperature T.sub.2 is set for the mixture of gas and ground material, which temperature is lower than T.sub.1, T.sub.2 possibly depending on the moisture content of the material, and in that when the minimum gas flow rate does not suffice for reaching the set temperature T.sub.2 with the temperature of the feed gas raised to the maximum of its range, then the flow rate Q.sub.2 of the gas fraction sent to the pre-drying means is increased by the amount necessary for reaching the temperature T.sub.2.
The invention also provides a system for grinding solid fuel material having a variable moisture content, and for drying said material, the system comprising grinding and drying apparatus, material feed means, pre-drying means disposed downstream from the feed means and feeding the apparatus with material, first injection means for injecting gas into the apparatus, second injection means for injecting gas into the pre-drying means, gas feed means, said gas being split into a first fraction feedin
REFERENCES:
patent: 3894344 (1975-07-01), Malcolm
patent: 4502227 (1985-03-01), Janusch
patent: 4592293 (1986-06-01), Toyama et al.
"Un Broyeur Unique Par Chaudiere en Chauffe Directe" by G. Vergniol (Jun. 1985) 2048 Revue Alstholm, No. 1 pp. 31-40.
"Rohrkugelmuhlen fur eine Steinkohlenstaubfeuerung mit direkter Einblasung" by Von W. Heitmuller, K. Straub and F. Thelen, VGB Kraftwerkstechnick 67 (May 1987) No. 12, pp. 1185-1192.
Bennet Henry A.
Gromada Denise L. F.
Stein Industrie
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