Claims:We Claim:
1. A process for determination of cross-leakage in a coke oven battery based on combustion gas analysis comprising:
analyzing gas samples from a heating wall for oxygen content to enable cross leakage determination; and
carrying out stoichiometric calculations based on the above analysis to thereby arrive at the percentage cross-leakage from respective points as indicator of battery health and refractory condition for timely preventive action, wherein percent infiltration of raw coke oven gas into heating flue gas is determined based on stoichiometric computations using the value of oxygen present in gas measured by analyzer.
2. The process for determination of cross-leakage in a coke oven battery as claimed in claim 1 comprising:
identifying the appropriate gas sampling points based on the heating systems of the different batteries and existing visual information;
collecting samples of combustion products during both zero cross leakage and cross leakage conditions for analyzing involving analyzer;
measuring oxygen levels by said analyzer in said flue gas samples collected from respective sampling points;

calculating the depletion of oxygen from zero cross leakage condition to cross leakage condition based on combustion stoichiometry, heating gas flow rates and raw gas composition by using an iterative method to arrive at the percentage cross-leakage from respective points as indicator of battery health and refractory condition for timely preventive action.
3. The process for the determination of cross-leakage in a coke oven battery as claimed in anyone of claims 1 or 2, wherein gas sample is drawn into the analyzer via a standard probe and hose connected to the input connection on the side panel of the analyzer.
4. The process for the determination of cross-leakage in a coke oven battery as claimed in anyone of claims 1 to 3, wherein said analysis of the flue gas is carried out with a portable flue gas analyzer capable of direct measurement of oxygen in flue gas.
5. The process for determination of cross-leakage in a coke oven battery as claimed in anyone of claims 1 to 4, wherein for oven-wise cross-leakage determination, waste gas samples from the regenerator sole flue are analyzed.
6. The process for determination of cross-leakage in a coke oven battery as claimed in anyone of claims 1 to 7, wherein the cross-leakage profile through its entire coking cycle are determined for a few ovens as required.

7. The process for determination of cross-leakage in a coke oven battery as claimed in anyone of claims 1 to 8, wherein a percent cross-leakage from oven over 6% is indicative of poor oven health/refractory condition needing maintenance/replacement.
Dated this 31st day of March, 2022
For STEEL AUTHORITY OF INDIA LIMITED
By their Agent

(ANSHUL SUNILKUMAR SAURASTRI) (IN/PA 3086)
KRISHNA & SAURASTRI ASSOCIATES LLP

, Description:FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
&
THE PATENTS RULES, 2003

COMPLETE SPECIFICATION
[SEE SECTION 10, RULE 13]

A PROCESS FOR DETERMINATION OF CROSS-LEAKAGE IN A COKE OVEN BATTERY BASED ON OXYGEN ANALYSIS IN COMBUSTION PRODUCTS;

STEEL AUTHORITY OF INDIA LIMITED, A GOVERNMENT OF INDIA ENTERPRISE, HAVING ITS ADDRESS AT RESEARCH & DEVELOPMENT CENTRE FOR IRON & STEEL, DORANDA, RANCHI-834002, STATE OF JHARKHAND, INDIA

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
TECHNICAL FIELD
[0001] The present invention relates to a process for determination of cross-leakages in a coke oven battery. More particularly, the present invention is directed to provide a quantitative process for determination of cross-leakage based on oxygen analysis in combustion products.
BACKGROUND OF THE INVENTION
[0002] It is well known in the art of coke production from coal that the coking process is carried out in sealed, narrow, externally heated chambers called ovens. Ovens are erected in batteries of approximately 60-80 ovens placed side by side, with heating walls between each oven. As the battery ages, cracks and fissures develop on the refractory wall separating the ovens from the heating walls leading to leakage of raw gas from the ovens to the heating walls and vice-versa. Cross-leakage of raw coke oven gas from the oven chambers to the heating walls not only leads to a loss of coke oven gas yield but it also significantly disturbs the pressure distribution throughout the heating system and leads to chimney emissions.
[0003] However, this cross leakage is an early indicator of battery health and refractory condition. Thus, determination and grading of cross leakage can be an important part of maintenance strategies that eliminate or delay capital expenditure on new batteries or major battery refurbishment with minimum effect on production due to downtime.
[0004] Conventionally, cross- leakage has been visually estimated in terms of chimney smoking or vertical flue inspection. However, these methods are qualitative and subjective in nature. Moreover, an early detection of cross-leakage is a pre-requisite for timely preventive action and chimney smoking can be visually detected only at an advanced stage of cross-leakage by which time significant damage had been done.
[0005] A technical paper titled ‘Condition monitoring of coke oven heating walls using waste gas analysis’ presented at the 8th European Conference on Coal Research and Its Applications (ECCRIA) conference, Leeds, United Kingdom, September 6-8, 2010 by M. Saiepour, S. Johnston, M. Zandi; Swinden Technology Centre, United Kingdom, disclosed research aimed at reducing emissions, maximizing energy efficiency and improving performance of coke oven underfiring heating, wherein waste gas measurements at individual walls have been undertaken for the detection of through-wall leakage and assessment of its severity.
[0006] The research has shown that the measurements of CO, O2 and methane may be used as indicators of through-wall leakage. The results have shown that for a wall with high severity leakage, after charging, the O2 value can be as low as 1.5% (compared to approximately 8% where there is low leakage) and CO can be at least 4,500 ppm compared to a low leakage value of approximately 100 ppm. During charging of ovens with severe through-wall leakage, much higher values of CO (approx 18,000 ppm) and methane (approx 1,300 ppm) have been measured, while O2 dropped to 0%.
[0007] Further, a process is known for determination of cross-leakage based on the analysis of CO2 in the combustion products. However, this requires the use of a near infrared (NIR) based CO2 analyser which is costly and bulky.
[0008] There has been therefore a need in the art to develop a quantitative method for precise determination of cross-leakage in a coke oven battery based on simple analysis tools that are readily available in a Steel Plant which would favour regular condition monitoring of the health of the heating walls of ovens and foretell preventive measures necessary.
SUMMARY OF THE INVENTION
[0009] An aspect of the present invention is directed to a process for determination of cross-leakage in a coke oven battery based on combustion product analysis comprising the step of analyzing gas samples from a heating wall both during zero cross leakage and cross leakage conditions to enable cross leakage determination, and step of carrying out stoichiometric calculations based on the above analysis to thereby arrive at the percentage cross-leakage from respective points as indicator of battery health and refractory condition for timely preventive action. The percent infiltration of raw coke oven gas into heating flue gas is determined based on stoichiometric computations using the value of oxygen present in gas measured by an oxygen analyzer.
[0010] A further aspect of the present invention is directed at a process for determination of cross-leakage in a coke oven battery comprising: identifying the appropriate gas sampling points based on the heating systems of the different batteries and existing visual information; collecting samples of combustion products during both zero cross leakage and cross leakage conditions for analyzing involving analyzer; measuring oxygen levels by said analyzer in said flue gas samples collected from respective sampling points; calculating the depletion of oxygen from zero cross leakage condition to cross leakage condition based on combustion stoichiometry, heating gas flow rates and raw gas composition by using an iterative method to arrive at the percentage cross-leakage from respective points as indicator of battery health and refractory condition for timely preventive action.
[0011] A still further aspect of the present invention is directed to a quantitative process for the determination of cross-leakage in a coke oven battery, wherein gas sample is drawn into the analyzer via a standard probe and hose connected to the input connection on the side panel of the analyzer.
[0012] Yet another aspect of the present invention is directed to a quantitative process for the determination of cross-leakage in a coke oven battery, wherein said analysis of the flue gas is carried out with a portable flue gas analyzer capable of measuring oxygen in flue gas.
[0013] In said process for the determination of cross-leakage in a coke oven battery, samples of flue gas is drawn to said analyzer with probes having required attachments.
[0014] Importantly, according to the quantitative process for the determination of cross-leakage in a coke oven battery of the present invention, for oven-wise cross-leakage determination, waste gas samples from the regenerator sole flue are analyzed.
[0015] According to yet another aspect of the present invention is directed to a quantitative process for the determination of cross-leakage in a coke oven battery, wherein percent infiltration of raw coke oven gas into heating flue gas is determined based on stoichiometric computations using the value of O2 present in waste gas measured by analyzer.
[0016] A further aspect of the present invention is directed to a quantitative process for the determination of cross-leakage in a coke oven battery wherein the cross-leakage profile through its entire coking cycle are determined for a few ovens as required.
[0017] A still further aspect of the present invention is directed to a quantitative process for the determination of cross-leakage in a coke oven battery, wherein a percent cross-leakage from oven/battery greater than 6% is indicative of poor battery health/refractory condition needing maintenance/replacement.
[0018] The objects and advantages of the present invention are described in greater details in the following description.
DETAILED DESCRIPTION
[0019] In the following description, for the purpose of explanation, specific details are set forth in order to provide an understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known structures are shown in diagram form to facilitate describing the invention. One skilled in the art will recognize that embodiments of the present invention, some of which are described below, may be incorporated into several applications.
[0020] While this invention is susceptible of embodiments in many different forms, a preferred embodiment of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspects of the invention to the embodiment illustrated.
[0021] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein may be made without departing from the scope of the invention.
[0022] The present invention aims at providing a quantitative process for determination of cross-leakage based on combustion gas analysis, the heating systems of coke oven battery is studied with a view to have an idea of the heating regime and to identify the appropriate gas sampling points. Based on the study of the heating system, points were identified for the sampling of waste gas to determine cross-leakage. For the determination of cross-leakage from individual ovens, waste gas samples were drawn from the regenerator sole flue of particular ovens. An oxygen analyzer is used for the analysis of the flue gas. The gas sample drawn into the analyser via a standard probe and hose connected to the input connection on the side panel of the analyser.
[0023] Stoichiometric equations are developed based on the chemical composition of the heating gas – coke oven / blast furnace / mixed gas. For the first few experiments the end heating walls where ingress can occur only from one side, were selected. After the first trial for validation, heating walls were selected based on the progress of coking in adjacent ovens. Mostly, empty ovens and corresponding freshly charged ovens were selected to get the maximum cross-leakage values.
[0024] The zero cross leakage condition is when the coal has been heated/carbonised for about two thirds of its total coking cycle, gas evolution becomes negligible as most of the gases have evolved and thus, there is zero cross-leakage after this period. So, this is a no cross-leakage period, where gas evolution has been completed. The combustion products from this heating wall during this period will be free from the content of combustion products due to cross-leakage. Similarly, the situation of zero cross leakage condition is noticed after the coke from an oven has been pushed out and before it is filled with coal again, there will be negligible cross-leakage to the adjacent heating wall considering the other side adjacent oven is already past half of its heating cycle as per the heating schedule, and gas generation has reduced considerably even from this oven.
[0025] Cross-leakage from individual heating walls were determined by sampling and analysis of the combustion products from the waste heat box of individual heating walls when the adjacent oven is empty and just after the oven has been charged. The real time cross-leakage of raw gas from the oven to the heating wall in Nm3 per hour is then calculated on the basis of difference in excess air coefficient obtained in these two situations and the flow rate of heating gas in the heating walls. This is then converted to percentage cross-leakage using the value of raw gas generation from the oven.
[0026] Cross-leakage manifests itself in the form of oxygen depletion in the combustion products. After knowing the oxygen content in combustion products for the particular coke oven battery heating regime for zero cross-leakage situations. The depletion in oxygen content in combustion products from specific heating chambers is converted to percentage cross-leakage (% of raw gas that has leaked from the oven to the heating chamber) based on a formula derived from the combustion stoichiometry, heating gas flow rates and raw gas composition and by using an iterative method.
[0027] The process of determining the cross-leakage in coke oven batteries according to the present invention is distinguished from the prior research studies in the sense that it is based on analysis of waste gas in terms of O2 content during cross leakage and non-cross leakage conditions and using stoichiometrical equations to determine percentage cross-leakage based on these analysis results and overcome the limitations and disadvantages of the prior art method. The oxygen content in the current invention is determined using a simpletools readily available in a steel plant like a hand held oxygen analyzer based on electro-chemical sensor.
[0028] According to an example embodiment of the present invention, cross-leakage from individual heating walls is determined by sampling and analysis of the combustion products from the waste heat box of individual heating walls when the adjacent oven is empty and just after the oven has been charged. The real time cross-leakage of raw gas from the oven to the heating wall in Nm3 per hour is then calculated on the basis of difference in oxygen content obtained in these two situations and the flow rate of heating gas in the heating walls. This is then converted to percentage cross-leakage using the value of raw gas generation from the oven. The calculations were carried out using the following battery data:
Basis of calculation:
Number of Ovens in Battery: 74 No.
Oven charging: 104 Nos./ day
Quantity of coal charged: 30. 56 t/oven
42.9 t/oven/ day
1.8 t/oven /h
Coke Oven Gas generation:
Quantity: 42, 365 Nm3/h/battery
572.5Nm3/h/oven
Net calorific value: 4,256kcal/Nm3

Sample results:

[0029] It is thus possible by way of the present invention to providing a process for the determination of cross-leakage in a coke oven battery based on the combustion gas analysis of samples collected from selected points at the regenerator base flue for individual oven which is analyzed in an analyzer both zero cross leakage and cross leakage conditions to find the values of O2 present in flue gas and using this value in an equation developed using stoichiometric calculations, the percentage infiltration or cross leakage can be ascertained. The cross-leakage measure thus obtained is an indicator of the health of the oven heating walls and refractory walls facilitating decisions relating to preventive maintenance planning and capital expenditure on vital equipments as well as to conform to emission norms.
[0030] The process would favour reducing loss of coke oven gas, save energy consumption in coke making process and facilitate decision on maintenance/replacement planning for basic equipment’s.
[0031] Although there has been shown and described the preferred embodiment of the present invention, it will be readily apparent to those skilled in the art that modifications may be made thereto which do not exceed the scope of the appended claims. Therefore, the scope of the invention is only to be limited by the following claims.