Process for the recovery of coke oven waste heat

This invention is directed to a process for making coke and recovering the heat therefrom for preheating the firing gas to the coke oven. The process involves the use of the coke oven firing gas to extract the sensible heat from the hot coke from the coking oven to both preheat the firing gas for the coke oven and cool the hot coke. Significant economies are achieved in the two-fold function of coke production and heat recovery in accordance with the method disclosed.

BACKGROUND OF THE INVENTION 
This invention relates to a process for making coke from coal and, more 
particularly, to the recovery of coke oven waste heat in a complete coke 
production process. 
In conventional coke production processes, coking coal is fed into coke 
ovens where it is heated in the absence of air to transform the coal to 
coke. Coking ovens typically include a regenerator chamber below the oven 
where combustion air is heated prior to being mixed with the firing gas 
used to heat the coke ovens. On completion of the coking process, the hot 
coke which is at a temperature of about 1000.degree. C. is removed from 
the oven and taken to a quenching tower where it is sprayed with water to 
cool it. 
The hot coke coming from the coking ovens has a significant quantity of 
sensible heat. Processes are known for utilizing that sensible heat. For 
example, in German Pat. Nos. 24 34 872 and 24 15 758, there are disclosed 
processes wherein the hot coke is cooled and the sensible heat of the hot 
coke is used either directly or indirectly to dry and/or preheat the 
coking coal charge. 
SUMMARY OF THE INVENTION 
It is among the principal objects of this invention to provide a more 
economical recovery of the sensible heat of the hot coke. 
This invention consists of a unique method of coke production and heat 
recovery therefrom. The invention provides a more economical recovery of 
the sensible heat of the hot coke than has heretofore been available. In 
accordance with the principles of this invention, the sensible heat of the 
hot coke is extracted by the firing gas used to heat the coke ovens and 
that heat is used to heat the firing gas prior to is introduction into the 
coke ovens. 
In accordance with the process of this invention, the hot coke taken from 
the coking oven is fed to a dry coke cooler. In the dry coke cooler, the 
bottom firing gas for the coking ovens is passed either directly or 
indirectly through the hot coke. The bottom firing gas thus extracts the 
sensible heat from the hot coke in the cooler which preheats the firing 
gas for its introduction into the coke oven. At the same time, the firing 
gas passing through the dry cooler serves to cool the hot coke. The 
process of this invention makes it possible to design the regenerator of 
the coke oven considerably smaller than usual since it is required only 
for preheating the combustion air, the firing gas having already been 
preheated by the heat of the hot coke in the dry coke cooler. 
It has also been found that the sensible heat of the hot coke is always 
greater than that required for preheating the firing gas. Therefore, 
depending on the loads, the firing gas can always be preheated to a 
desired temperature of at least about 900.degree. C. The temperature of 
the coke taken from the dry coke cooler will then vary. However, these 
temperature variations are of little significance in the process since the 
dry coke is then taken to a quenching tower where such variations can be 
easily accommodated. It is also possible to heat the firing gas in the dry 
coke cooler to a temperature greater than that necessary for preheating 
the firing gas making it possible to use the excess heat contained in the 
firing gas for heating the combustion air for the coke oven. This makes it 
possible to design the regenerator even smaller. 
In accordance with a presently preferred form of this invention, coking 
coal is fed to a coal preheater where it is heated to a temperature in the 
range of about 150.degree. to 250.degree. C. The heat for the coal 
preheater is supplied by the flue gas from the coke oven as is known in 
the art. The dry heated coal is then fed to the coke oven. The oven is 
heated by a mixture of combustion air which is heated in the regenerator 
portion of the coke oven and the firing gas. The hot coke is then taken 
from the coke oven at a temperature of about 1000.degree. C. and is 
transferred to a dry coke cooler. In the dry coke cooler, the firing gas 
used to heat the coke oven is passed therethrough to extract the sensible 
heat from the dry hot coke. The firing gas exits the coke cooler and is 
fed to the coke oven where it is mixed with the combustion air heated in 
the regenerator to fire the oven. The dry coke from the coke cooler is 
then taken to a quenching tower where it is sprayed with water to cool it. 
If the firing gas employed in the process is inert with respect to the hot 
coke, it can be passed directly through and over the hot coke thereby 
eliminating any equipment requirements for primary and secondary gas 
circulation thus reducing equipment costs.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the attached drawing, the coking coal which is at ambient 
temperature is fed to a coal preheater 10. The coal preheater is 
preferably heated by flue gas from the coke oven 12 via the line 14. In 
the coal preheater 10, the coking coal is dried and discharged via path 16 
at a temperature in the range of 150.degree. to 250.degree. C., preferably 
about 200.degree. C. The dry coal is then fed into the oven portion 18 of 
the coke oven 12. After the coal has been in the oven 12 a sufficient time 
to convert it to coke, it is removed from the oven and passed to a dry 
coke cooler 20. 
The coke taken from the coke oven 12 is at a temperature of about 
1000.degree. C. The firing gas for the coke oven enters the dry coke 
cooler 20 via line 22 where it is heated by the sensible heat of the hot 
coke. In a presently preferred form of the invention, the firing gas is 
blast furnace stack gas. The use of blast furnace stack gas is 
particularly advantageous, first because it is readily available at any 
steel mill, and second because it is substantially inert with respect to 
the dry coke. Therefore, it can be passed directly through and over the 
hot coke without igniting. If a non-inert firing gas is used secondary 
heat transfer equipment for circulating the firing gas through the cooler 
20 to extract the sensible heat of the hot coke without directly 
contacting the coke is required. Thus, the use of blast furnace stack gas 
provides an optimum process. 
The firing gas exits the dry coke cooler 20 via line 24 and is then fed to 
the bottom of the coke oven 12. Combustion air enters the regenerator 
section 26 of the coke oven where it is heated and thereafter mixed with 
the preheated firing gas. Since the firing gas has been preheated, the 
combustion air is not required to heat the firing gas thus making it 
possible to reduce the size of the regenerator of the coke oven. In 
addition, since this process permits the use of a smaller regenerator, the 
flue gas leaving the coke oven via line 14 is at a higher temperature than 
usual. Thus, this high temperature flue gas may advantageously be utilized 
for drying and preheating the coking coal to make full use of all of the 
waste heat from the coking oven. 
The coke in the dry coke cooler 20 is cooled by the firing or stack gas 
passing therethrough. As stated above, the extracted sensible heat heats 
the firing gas prior to its introduction into the coke oven 12. The coke 
is then removed from the cooler 20 and is transferred to a quenching 
station via path 28, for example, a quenching tower 30 where it is sprayed 
with water to cool it below ignition temperature. After quenching, the 
coke may be sorted and transferred for storage or use in accordance with 
conventional applications. 
In one alternative embodiment of the invention, a portion of the waste gas 
from the coal preheater 10 is mixed with the stack gas prior to its 
passing through the dry coke cooler 20. This is accomplished by passing 
the waste gas through a line 32 to mix it with the stack gas before the 
gas is fed to the dry coke cooler. A valve 34 is placed in line to 
selectively control the use of the waste gas as desired. By mixing the 
waste gas with the stack gas, the composition and combustion value of the 
firing gas may be controlled.