GB2064081A

GB2064081A - A Method of Heating Coke Ovens

Info

Publication number: GB2064081A
Application number: GB8026701A
Authority: GB
Original assignee: Dr C Otto and Co GmbH
Current assignee: Dr C Otto and Co GmbH
Priority date: 1979-11-24
Filing date: 1980-08-15
Publication date: 1981-06-10
Also published as: GB2064081B; CA1171021A; JPS5676484A; AU6015580A; DE2947447A1; NL8004129A; CA1143724A; FR2470150B1; IT8049089A0; AR223532A1; IT1128120B; BR8005493A; IN152657B; DE2947447C2; FR2470150A1; BE884942A; ZA805191B; AU530601B2

Abstract

This invention relates to a method of heating coke ovens with a rich gas mixed with varying proportions of relatively lean gas, with regenerative heat exchange between the combustion air and burnt gases only. In the method the pressure of the gas supplied to the burners is kept at a constant value selected to correspond to the maximum admixture of lean gas in the mixed gas and any reduction in the quantity of lean gas supplied is compensated for by cutting off heating for an interval within each regenerative half-period, in which the reduction of lean gas occurs. In this way the heat supplied during a regenerative half-period can be controlled to a predetermined value.

Description

SPECIFICATION A Method of Heating Coke Ovens The invention relates to a method of heating coke ovens with a by-product gas mixed with varying proportions of relatively lean gas, with regenerative heat exchange between the combustion air and burnt gases only.

During the operation of coke ovens at or near steelworks or other installations, gas having a lower calorific value than by-product gas is produced, often in varying amounts. Attempts are therefore made to use the coal by-product gas for other purposes. The coke oven can be operated with a mixture of appropriate rich gas and relatively lean gas; the rich gas can be diluted with the lean gas provided the calorific value of the mixture does not drop lower than 2500, and preferably not lower than 3000 kcal/m3. Any further reduction in calorific value will reduce the thermal efficiency; the preheating by regenerators, which is normal for lean gas, will not occur, and the method must also be suitable for an oven using rich gas only.

Broadly the invention relates to coke ovens where such a mixed gas is conveyed in conventional manner through the rich-gas heating system. However, owing to the larger quantities and mass of gas, the pressures need to be greater than when rich gas is used only. The pressures are kept at a minimum, to avoid the risk of gas leaking through the change-over and shutting-off facilities. Preferably in practice, the pressures in the distributing pipe are about 120 to 1 50 mm water column and below 100 mm WC in the "nozzle pipeline" extending in the cellar in underjet ovens.

If the pressures are set for a mixed gas containing a maximum amount of lean gas and if the nozzles of a heating wall are bored until the pressure in the nozzle pipeline is about 90 mm WC, the drop in pressure on changing over to heating with rich gas only would be so great that the rich gas could not be efficiently distributed among the individual burners on the heating wall.

It is of course impossible to adapt the nozzle cross-section in response to every change in gas mixture or to heating with rich gas only.

The present invention consists in a method of heating coke ovens with a by-product gas mixed with varying proportions of relatively lean gas, with regenerative heat exchange between the combustion air and burnt gases only, including keeping the pressure in the distributing pipe at a constant value corresponding to the maximum admixture of lean gas to form the mixed gas, and if the addition of lean gas is reduced or stopped, compensating for the increased amount of heat supplied to the ovens by cutting off the heating for an interval within each regenerative halfperiod, in which the addition of lean gas is reduced or stopped.

The length of the interval will be made longer or shorter depending on whether the calorific value of the mixed gas rises or falls as a result of reduced admixture with lean gas. This mode of operation allows optimum adjustment to be made to all the properties of the gas mixture without changing the cross-section of the nozzles or other regulating means, which are the main components which control gas distribution. It is only necessary to construct the change-over device so that the length of the interval during the regenerative half-periods can be varied.

Accordingly, if the calorific value of the mixed gas changes during operation, this device, which is disposed at the change-over winch merely needs to be adjusted; either the timing of the interval or its duration can be changed.

There are known methods of causing pauses in heating during each regenerative half-period. For example, a pause can be created by closing the gas cocks and then bringing into position a flue gas throttling device disposed in the distributing pipe between the common waste-gas flue and the chimney to reduce the suction in the common waste-gas flue.

Alternatively, the pause can be obtained by first closing the gas cocks and then moving all the air valves and flue-gas valves to a central position.

The invention may be performed in a number of ways one example of which will be illustrated by the following numerical example: Given calorific value of rich gas: He=4500 kcal/Nm3 Weight: =0.4 kg/Nm3 Calorific value of lean gas: He=700 kcal/Nm3 Weight: =1.2 kg/Nm3 In order to obtain mixed gas having a calorific value of He=3000 kcal/Nm3, using the given densities and calorific values of rich and lean gas, about 60% rich gas must be mixed with 40% lean gas. The weight of the mixed gas will be 0.72 kg/Nm3.

The amount of heat conveyed during mixed gas heating must be the same as when rich gas alone is used. The pressure of mixed gas in the row of rich-gas nozzles is 90 mm WC, whereas if rich gas along is used over a whole half period, the pressure will be 22 mm WC. This pressure is too low if efficient distribution of the rich gas among the individual burners on the heating wall is to occur. In order to raise the pressure to 90 mm WC, the volumetric flow of gas must be increased by a factor of about 2, i.e. twice the amount of rich gas, than is necessary to provide the required heat, in order to keep the pressure along the row of nozzles constant at 90 mm WC.

If the regenerative half-period is 30 minutes, then 15 minutes' of heating with rich gas along and 1 5 minutes' pause will supply the same heat in each regenerative half-period as is supplied over the whole period of mixed-gas heating in the above example. If the mixed gas used for heating has a higher calorific value, i.e., if a smaller proportion of lean gas is mixed with the rich gas, the pauses in heating will be correspondingly shorter.

Claims

1. A method of heating coke ovens with a byproduct gas mixed with varying proportions of relatively lean gas, with regenerative heat exchange between the combustion air and burnt gases only, including keeping the pressure in the distributing pipe at a constant value corresponding to the maximum admixture of lean gas to form the mixed gas, and if the addition of lean gas is reduced or stopped, compensating for the amount of heat supplied to the ovens by cutting off the heating for an interval within each regenerative half-period, in which the addition of lean gas is reduced or stopped.

2. A method as claimed in claim 1, wherein the length of the interval is made longer or shorter in accordance with any increase or decrease in the calorific value of the mixed gas resulting from reduced admixture of lean gas.

3. A method as claimed in claim 1 or claim 2, wherein heating is cut off for more than one interval in at least one regenerative half-period.

4. A method as claimed in any one of the preceding claims wherein the gas pressure in the distributing pipe lies in the range 80 to 100 mm WC.

5. A method of heating coke ovens with a byproduct gas mixed with varying proportions of relatively lean gas, with regenerative heat exchange, between the combustion air and burnt gases only, substantially as hereinbefore described.