Title of Invention

A METHOD FOR DETERMINATION OF COKING INDEX AND EVALUATION OF PROGRESS OF CARBONIZATION IN EACH OVEN.

Abstract

A method for determination of coking index of each coke oven in a battery for detection of coke readiness by evaluation of the actual progress of carbonisation in each oven The method comprises the steps of determining the peak tenvrature (tmax_temp) from raw gas temperature profile for each oven; determining the time (tmax_time) to reach peak temperature or carbonization period from the equation: tmax_time (i) = now_time - last_time (i); where 'now_time' is the time when the temperature peak is detected and 'last_time ' (i) is the last charging time of oven (i); determining the coking period from the equation : coking period = next_time (i) - last time (i): where 'next_time' is next pushing time and 'last_time' is the last charging time; and determining the coking index using data generated from steps i, ii and iii based on : Coking index = Coking period Carbonisation period

Full Text

Field of the invention : The present invention relates to a method for determination of the coking index of coke ovens in a battery by evaluation of the actual progress of carbonisation in each oven. More particularly the invention relates to maintenance of the coking index in the battery by controlling the heating gas flow. Description of known art: In a coke plant, coal is coked by destructive distillation ie, without combustion. This process is carried out in sealed, narrow, externally heated chambers called ovens from which the residue, coke, is subsequently pushed, quenched, and screened for use as fuel in the blast furnace. Ovens are erected in batteries of approximately 60-80 ovens placed side by side, with heating walls between each oven. The coal is charged from the top in each oven. The coking of the coal proceeds from both sides and the carbonisation is completed when the two layers of the coke meet at the centre. Subsequently, some additional time known as the soaking time is given to improve the coke quality before the coke is ready for pushing. The optimum soaking time required depends on the quality of the coal blend and other battery specific conditions. Conventionally, the time at which an oven is ready to be pushed (coking period) is determined on the basis of the heating wall temperatures and is the same for all ovens in a battery irrespective of the dynamic conditions prevailing in each oven. The heating wall temperature is itself determined by manually measuring the temperature of a few vertical flues, once daily - a method that is at once subjective and unrepresentative. Since there is no way to determine the actual progress of carbonisation in each oven, a safety margin in the form of an excess of soaking time is included in the conventional coking period to prevent the pushing of coke before it is ready. Hence waste of heat energy results without improving the coke quality. 2 Object of the Invention : Thus the main object of the present invention is to provide a method for detection of coking index of coke ovens in a battery for determination of coke readiness by evaluation of the actual progress of carbonisation in each oven. A further object is to provide a method for maintaining the optimum coking index by controlling the heating gas flow to achievegreater efficiency of coke ovens. Summary of Invention Thus according to main aspect of the present invention there is provided a method for determination of coking index of each coke oven in a battery for detection of coke readiness by evaluation of the actual progress of carbonisation in each oven comprising: i) determining the peak temperature (tmax_temp) from raw gas temperature profile for each oven; ii) determining the time (tmax_time) to reach peak temperature or carbonization period based on the equation: tmax_time (i) = now_time - last_time (i); where *now_time' is the time when the temperature peak is detected and 'last time (i)' is the last charging time of oven ; iii) determining the coking period based on the equation : Coking period = next_time (i) - last time (i)- where 'next_time ' is next pushing time and last_time is the last charging time; and iv) determining the coking index using data generated from steps i, iiand iii based on the equation : Coking index = Coking period Carbonisation period 3 Details of the Invention : According to the method of present invention the temperature of the raw gas is determined on-line by a computer program based on the various equations listed above, and stored in a database. The temperature is continuously compared with the data available and the peak temperature is determined as the highest temperature level achieved. The time to reach this temperature is also determined and stored in database. These data are then used to calculate the coking index for each oven of the battery and the average coking index of the battery. This is then compared with the optimum coking index of the battery. The optimum range of coking index is predetermined based on the quality of coke obtained at different coking indices. The process coking index is then maintained at the optimum level by controlling the heat gas flow in the feed back mode. DETERMINING THE PEAK TEMPERATURE (TMAX TEMP) In the method of the present invention, the means for measuring the temperature of the raw gas (distillation gas) on-line for each oven are through-thermocouples inserted in the gas off-takes known as ascension pipes. For the purpose Chromel-AIumel thermocouples are used. The thermocouples are put inside protective stainless steel sheaths to protect against the corrosive atmosphere inside the ascension pipes. The millivolt signal generated by the thermocouple is conditioned properly and through method hardware namely temperature transmitters to generate the temperature profile of each oven as the carbonisation proceeds inside. The raw gas temperature profile has a definite relationship with the progress of carbonisation and distinctly indicates the time at which the carbonisation is completed, i.e., the time at which the two coke layers meet at the centre of the oven. This is indicated in the form of a temperature peak. For the detection of the said temperature peak the temperature of the raw gas is determined at first and then the peak calculated from the same. As the coal is charged into the oven, it gradually softens and goes into a liquid state and finally solidifies to form coke, all the while evolving a distillation gas known as raw gas. 4 This process of coke formation starts from the two sides of the oven (as each oven is externally heated from the sides) in the form of coke layers. As coking proceeds, the temperature of the raw gas goes on increasing and culminates in the form of a peak signifying the meeting of the coke layers at the centre of the oven. The temperature of the raw gas is measured by installing thermocouples inside the gas off takes (ascension pipes) of each oven. This temperature data is then communicated to the central PLC where it is recorded in the form of a continuous data base. A high-end Programmable logic controller PLC is used for the purpose. The peak temperature is detected through a PC based software programme. The software continuously accesses the raw gas temperature from the continuous data base, compares the previous temperature (rgas_temp (i) ) with the current temperature(last__temp), and, if the current temperature is lower than the previous temperature, designates the previous temperature as the peak temperature (tmax_temp) and feeds it back to the PLC. Thus the peak temperature is determined. DETERMINING THE TIME (TMAX TIME) Each of the ovens is provided with oven identification method which detects and times the occurrence of pushing and charging of each oven. This data is communicated to the central PLC where it is recorded as event data base. The PC based software for coking index calculation accesses this data from the PLC and calculates the time taken to reach peak raw gas temperature for a particular oven (i) as : tmax_time (i) = now_time - last_time (i) where nowtime is the time when the temperature peak is detected and last_time (i) is the last charging time of oven (i) 5 DETERMINING THE COKING INDEX The timax time is also known as the carbonization period. After carbonization is completed, some more time is given before the coke is pushed. This additional time is known as the soaking period. Thus, coking period, ie, the total time from coal charging to coke pushing is the sum of carbonization period and soaking period: Coking period = Carbonisation period + Soaking period DETERMINING THE COKING PERIOD For determining the coking period, the scheduled next pushing time (next_ time (i) ) of (he particular oven is required. This is obtained from the dynamic oven scheduling model as described in our copending application and incorporated here by way of reference. The coking period is then calculated as : Coking period = nexttime (i) - last time (i) The soaking period that is required for optimum coke quality depends on coal quality and battery conditions. For a particular battery, it is specified in the form of a ratio known as the coking index: 6 This ratio (coking index) is then maintained throughout the battery by controlling the heating gas flow. The control of coking index is done in the feed-back mode. Every 20 minutes, (i.e. after each reversal) the average coking index of all the ovens is calculated. If the average coking index is below or above the predetermined optimum range of the battery, the gas flow is increased or decreased (by 0.8% in our case) respectively. For e.g., if the optimum range of coking index for a battery lies between 1.32 and 1.35 and if the actual value of average coking index after a particular reversal is 1.37, the gas flow is decreased 0.8%. The effect of this decrease will be reflected in the average coking index calculated at the next reversal (Feed back control). Here, it may be mentioned that the optimum coking index for a battery signifies the coking period beyond which there is no appreciable improvement in coke quality. Tn a coke oven battery, the oven walls are heated by burning fuel gas in a series of 28 heating flues built in each one of the oven walls. During one heating cycle, combustion takes place in the odd heating flues (1, 3, 5 etc.), even no. flues (2, 4, 6, 8 etc.) being the exhaust flues. At regular interval reversal takes place when the even numbered flues become the combustion flues and the odd numbered ones the exhaust flues. This is taken care of by the reversing gear. Reversing is carried out at regular intervals of 20 minutes. With the help of the coke readiness determination process ie coking index determination the amount of gas flow required for achieving optimum coking index is regulated. Thus, the gas earlier being wasted by heating of the oven beyond its optimum coking index is avoided. The invention is illustrated by the following non limiting exemplary illustrations 7 Brief Description of Accompanying drawings Figure 1 is a graphical representation of the temperature profile of raw gas with time for determination of tmax_temp, tmax_time, coking index Figure 2 : Flow diagram for determination of coking index. Detailed description of the accompanying drawings Figure 1: The temperature profile of the raw gas in an oven is provided as function of time and the peaks and nadirs are depicted. 1 denotes the tmax_temp which is the highest peak raw gas temperature achieved and is thus the temperature peak. The time to reach the said peak is tmax_time (2) i.e. the carbonisation period. The pushing and charging points are denoted as 3 and 4 respectively. The coking period is denoted as 5 Figure 2. As shown in the flow diagram the method starts from coking for each oven and the raw gas temperature (r gas_temp)is measured continuously and fed and compared with those from the continuous data base. The tmax_temp is then calculated. If the last temp is less than the rgas_temp at present then the tmax_temp is reached. The pushing time is also recorded and compared from the event data base. The time to reach the temperature peak or tmaxtime is calculated as the difference in the time when such temperature is reached and the last charging time. Thus tmax_time = nowtime - last_time. Then the next pushing time (next_time) is also recorded and compared with the event database. The coking index is then determined as cindex = ( next_time - last_time/ tmaxtime. In this manner the coking index of each oven is calculated and then the mean gives the coking index of the whole battery. 8 We claim: 1. A method for determination of coking index of each coke oven in a battery for detection of coke readiness by evaluation of the actual progress of carbonisation in each oven comprising the steps of: i) determining the peak temperature (tmax_temp) from raw gas temperature profile for each oven; ii) determining the time (tmaxtime) to reach peak, temperature or carbonization period from the equation: tmax_time (i) = now_time - lasttime (i); where 'now_time' is the time when the temperature peak is detected and 'lasttime ' (i) is the last charging time of oven (i); iii) determining the coking period from the equation : coking period = next_time (i) - last time (i): where 'next_time' is next pushing time and 'last_time' is the last charging time; and iv) determining the coking index using data generated from steps i, ii and iii based on : Coking index = Coking period Carbonisation period 2. A method as claimed in claim 1 wherein the temperature of the raw gas or the distillation gas in each oven is measured on line by means comprising thermocouple inserted in the ascension pipes. 3. A method as claimed in claim 1 or 2 wherein the said raw gas temperature is communicated to the central high-end Programmable logic controller PLC (PLC) where it is recorded in the form of continuous data base. 4. A method as claimed in any preceding claim wherein the peak temperature is detected through a PC based software program and feeding it back to the PLC. 9 5. A method as claimed in claim 4 wherein the peak temperature is detected by continuously accessing the raw gas temperature from the continuous data base, comparing the previous temperature (rgas_temp) with the current temperature (last_temp (i), and, if the current temperature is lower than the previous temperature, designating the previous temperature as the peak temperature (tmax_temp). 6. A method as claimed in any preceding claim wherein each of the ovens is provided with oven identification system which detects and times the occurrence of pushing and charging of each oven and communicates the data to the central PLC where it is recorded as event data base. 7. A method as claimed in claim any preceding claim wherein the data from the event database is used to generate the time taken to reach peak raw gas temperature (tmax_time) or the carbonization period for a particular oven. 8. A method as claimed in any preceding claim wherein the coking period which is the sum of carbonisation period and soaking period. 9. A method as claimed in any preceding claim wherein the coking index is maintained throughout the battery by controlling the heating gas flow in the feed-back mode comprising: calculating the average coking index of all the ovens; increasing/decreasing the gas flow if the average coking index is below or above the predetermined optimum range of the battery such that it will be reflected in the average coking index calculated at the next reversal. A method for determination of coking index of each coke oven in a battery for detection of coke readiness by evaluation of the actual progress of carbonisation in each oven The method comprises the steps of determining the peak tenvrature (tmax_temp) from raw gas temperature profile for each oven; determining the time (tmax_time) to reach peak temperature or carbonization period from the equation: tmax_time (i) = now_time - last_time (i); where 'now_time' is the time when the temperature peak is detected and 'last_time ' (i) is the last charging time of oven (i); determining the coking period from the equation : coking period = next_time (i) - last time (i): where 'next_time' is next pushing time and 'last_time' is the last charging time; and determining the coking index using data generated from steps i, ii and iii based on : Coking index = Coking period Carbonisation period

Documents:

00364-kol-2004-abstract.pdf

00364-kol-2004-claims.pdf

00364-kol-2004-correspondence.pdf

00364-kol-2004-description(complete).pdf

00364-kol-2004-drawings.pdf

00364-kol-2004-form-1.pdf

00364-kol-2004-form-18.pdf

00364-kol-2004-form-2.pdf

00364-kol-2004-form-3.pdf

00364-kol-2004-letters patent.pdf

00364-kol-2004-p.a.pdf

364-KOL-2004-(01-02-2012)-FORM-27.pdf

364-KOL-2004-FORM 27.pdf