FR2470150A1 - - Google Patents

Abstract

Method of heating a coke oven with a distillation gas to which a gas of low calorific value is added in variable proportions with only an exchange of regeneration heat between the combustion air and the flue gases. The pressure in the distribution line is maintained at a constant value which corresponds to the maximum addition of low calorific gas for the formation of mixed gas, and which takes into account the greater quantity of heat supplied to the furnace for a low addition or absence of addition of low calorific gas by introducing heating pauses during each regeneration half-period.

Description

i

  Process for heating coke ovens.

the present invention relates to a process for heating coke ovens with a distillation gas, to which is added in variable quantities a gas with low calorific value, with exchange of recovery heat only

between the combustion air and the burnt gases.

  In the coking plants of the steel factories or near

mity of these or other facilities in the operation

tation of which is produced in variable quantities a gas with low calorific value such as the gas of distillation of the coke ovens, one first endeavored to release the gas

  distillation of coal for other purposes. We can exploit

  ter coke ovens with a mixed gas composed of rich gas

  suitable and low calorific gas in weakening

sant the rich gas with the lean gas insofar as the mixed gas has a calorific value which does not become less than 2500, preferably 3000 kcal / m3. A further lowering of the calorific value would have an unfavorable influence on the thermal efficiency; otherwise the usual reheating using lean gas, in regenerators, is not carried out; also the process must be carried out with a

simple rich gas oven.

Mixed gas is also obtained in the usual way.

due to the rich gas heating system. Because of the larger quantities of gas and the higher specific weights of the gases, it is necessary to use higher pressures than for heating the rich gas alone. The lowest possible pressures are applied to avoid the danger of gas leaks through the reversing or shut-off valves. In practice, these pressures rise, for the distribution pipe, to approximately 120 to mm of water and are less than 100 mm of water in what is called the lance, which is found underground in the ovens with sole burners. If the pressures are suitable for a mixed gas with a maximum addition of gas with low calorific value and if the nozzles of a heating wall are bored so that a pressure of about 90 mm of water prevails in the lance, the pressure drops during a heating operation with the only rich gas, so that a judicious distribution of the quantity of rich gas over the various locations

combustion cements of the heating wall is impossible.

  It is not a question of adapting the diameter of the nozzle each time one changes and one passes to a heating with a mixed gas of a different composition or to

  heating with the only rich gas.

We will now describe the invention.

  The pressure in the distribution pipe is adjusted to a value which corresponds to the maximum addition of gases with low calorific value for the formation of mixed gas and the greatest amount of heat brought to the furnaces by weak additions or the absence of gas with low calorific value takes into account the introduction of breaks

  heating in each half regeneration period.

  The duration of the break is also evaluated as being longer or shorter, depending on whether the calorific value of the mixed gas has a high or low value as a result of small additions of gas with low calorific value. Thanks to this way of proceeding,

we can optimally adapt to all the characteristics

  gas combination without changing the section, important

aunt for distribution, nozzles and other organs

adjustment. It is only necessary to carry out the dispo-

  changeover so that longer or shorter heating breaks can be adjusted with it. When changing the calorific value of the mixed gas, it suffices in operation to change the arrangement provided for the inversion: this must either modify the pause, or

change its duration.

The measures for inserting breaks in the heating during each half-period of regeneration are known per se. For example, to insert the pause after closing the gas taps, a device for adjusting the flue gases can be placed between the flue collector and the chimney in a position for which

  only acts a weak suction in the collector.

  Another way of obtaining a heating break consists in first closing the gas taps and then bringing all the shutters to the central position.

heating than all burnt gas valves.

  The heating process according to the invention will now be explained in more detail using

of the numerical example below.

  Let the calorific value of the rich gas H = 4500 kcal / Nm3 the density of the rich gas = 0.4 kg / m3 the calorific value of the lean gas H = 700 kcal / Nm3 the density of the lean gas = 1.2 kg / Nm3 For achieve a calorific value of mixed gas

of Hu = 3000 kcal / Nm3 taking into account the values given above

above for the calorific values and the densities of the rich and lean gases, it is necessary to mix approximately 60% of rich gas with 40% Ie of lean gas. The density of the mixed gas

resulting is 0.72 kg / Nm3.

  To heat the mixed gas, bring the

  same amount of heat as for heating the rich gas.

  While the mixed gas would give a pressure of 90 mm of water in the jet of the rich gas nozzle, it would result in a

  22 mm pressure for exclusive heating of rich gas.

This would no longer suffice to ensure a good distribution of the quantity of rich gas over each of the combustion positions of the heating walls. To raise this pressure to 90 mm of water, the gas stream must be increased by an approximate proportion of 2, which means that twice the volume of rich gas must be brought to maintain the jet pressure of the nozzle at the value

constant of 90 mm of water.

A half-regeneration period of 30 min corresponds to an operating period of 15 min of the heating and a heating pause of 15 min, for the heating of the only rich gas, to ensure the same supply of heat in each half

regeneration period only for heating the mixed gas.

  For heating with a mixed gas with high calorific value, as well as with a rich gas with a low addition of a gas with low calorific value, this results in a duration

shorter of the heating break.

As goes without saying and as it already follows from the foregoing, the invention is in no way limited to that of its modes of application, no more than that of the modes of

realization of its various parts, having been more particularly

  rement envisaged; on the contrary, it embraces all its variants.

  In the foregoing description, it should be understood that

the pressure of 1 mm of water corresponds to 0.1 millibar and -a

  energy of kcal corresponds to 4180 joules.

Claims (2)

  1. A method of heating a coke oven with a distillation gas to which a gas with low calorific value is added in variable proportions with only one exchange of regenerative heat between the combustion air and the burnt gases, characterized in that that the pressure in the distribution line is maintained at a constant value which corresponds to the maximum addition of gas with low calorific value for the formation of mixed gas, and which takes account of the greater quantity of heat brought to the furnace for a low addition or absence of addition of low calorific gases by the introduction of breaks heating during each half regeneration period.   2. Method according to claim 1, characterized in that the break is evaluated longer or shorter depending on whether the calorific value of the mixed gas has a high or low value following a low addition of gas at low calorific power.