Claims:WE CLAIM:

1. A method for measurement of pH of coal slurry comprising the steps of :-
providing representative samples of coal slurry of quantity 0.5g in the form of 60 mesh coal;
mixing the coal sample with 5ml of distilled water in a digestion tube;
placing the mixture of coal and water sample in a Chemical Oxygen Demand (COD) Digester and the said mixture is heated to 150 deg C;
conditioning the mixture sample by maintaining it to 1500C for 2 hours;
cooling the said mixture indirectly using tap water to room temperature; transferring the mixture sample into a beaker for measurement of pH using probe,
wherein the heating system of COD digester ensures the availability of coal water slurry after heating at 150 deg C for 2 hours.

2. A method for measurement of pH of coal slurry as claimed in claim 1, wherein the digestion tube is a glass tube of thickness 1 mm and length 21 cm

3. An equation for prediction of pH of coal slurry as claimed in claim 1, wherein the pH of coal slurry is predicted using equation as :

pH of coal slurry = 11.92+0.380*Ash+0.657*Vitri+0.0826*Day-1.805*BAR-0.00529*(Vitri^2)-0.00908*Ash*Vitri-0.001358*Ash*Day-0.001154*Vitri*Day-0.08221*Day*BAR, ----------------------------- [3]
R sq: 96.74
Where
Ash- Ash in coal (%)
VM- Volatile matter of coal (%)
pH- pH of coal slurry
Vitri- Vitrinite in the coal (%)
Day- Time of storage at interval of 1 month
BAR- Basic to acid oxides ratio of coal

4. A method for measurement of pH of coal slurry as claimed in claim 1, wherein the pH values are correlated with hot strength of coke i.e. CSR. By a regression equation :
CSR = (-206.60-5.59*Vitrinite-25.92*Ash+29.79*pH+27.04*VM) -- [4]
R Square=0.97
Where:
VM- Volatile matter of coal (%)
pH- pH of coal slurry
Vitrinite- Vitrinite in the coal (%)
Ash- Ash in coal (%)

Dated: this 25th day of August, 2016


(N. K. Gupta)
Patent Agent,
Of NICHE,
For SAIL

To,
The Controller of Patents,
The Patent Office, Kolkata.
, Description:
A METHOD FOR MEASUREMENT OF pH OF COAL SLURRY

FIELD OF THE INVENTION:

The present invention relates to improved and easier method of measurement of pH of coal slurry to measure the level of oxidation in incoming coals. This invention concerns to the weathering status of incoming coal or coal stored in piles. The pH values are correlated with hot strength of coke, i.e., CSR. This may help to better utilization of weathered coal. By changing the blend composition the fluctuations in the coke quality because of weathered coal, can be minimized.

DESCRIPTION OF KNOWN ART:

It is well known that weathering has a profound effect on many important coal properties such as coking characteristics, slurry pH, floatability, tar yield, extractability, etc., as well as on coal utilization processes such as combustion, pyrolysis, gasification and liquefaction. This also affects its utilization process. However, since coal is a heterogeneous material and its chemical and physical properties differ markedly according to rank and seam, it is difficult to define reliable standard values for the degree of weathering in general. Therefore methods for determining the degree of weathering tend to provide relative values and have practical usefulness only if measured values can be calibrated against coal samples oxidized or weathered under carefully standardized conditions or against unoxidized coals such as freshly mined coals.

In the past, many different attempts have been made to measure the degree of weathering of a given coal sample. One of the more obvious approaches is perhaps to determine the oxygen content by oxidative, reductive, or pyrolytic methods since the weathering is essentially a process in which oxygen is being incorporated into the coal matrix. Alternatively, oxygen content can be measured directly by neutron activation analysis. However, the uptake of oxygen by a given coal can be offset to a significant degree by the concomitant loss of CO2, CO and H2O, thus making the net increase in oxygen content far from easily predictable. Moreover, most oxygen measurement techniques are notoriously time-consuming and unreliable.

Most of the method available to monitor weathering/oxidation of coal provides relative values. The use of such method is limited because initial values are not known.

Gray et al. (1976) suggested coal slurry pH measurement method as a technique to determine weathering status of coal. Hill et al. (1984) applied this method, but added surfactant (0.01 weight %) to increase wetting of coal with water.

When coal is weathered / oxidized it produces mixture of water soluble acid. These acids are Benzoic, Phthalic, mellitic and tri mellitic acids. Some results show increases in short chain carboxylic acid. In some cases anhydrides also formed. Rehydration of these anhydrides makes free acid. So, Yun et al. (1987) has developed an improved method which is applicable for a wide range of coals of different rank. In an initial weathering study for sub bituminous coal, pH determination at ambient temperature showed marked decrease in acidity. But studies with higher rank coal, pH measurement at room temp showed ambiguous results. This was due to the presence of anhydrides of phthalic acid or other aromatic acid. This anhydride removes the acidic proton and resulted in very small change in pH. Therefore, they developed a method in which oxidized coal are rehydrated at 150 deg C in a Parr Digestion Bomb. Temperature 150 deg C was selected to allow high enough temperature for restoring the acidity while, limiting the pressure build up inside the Bomb.

In SAIL plants the above mentioned method is not in practice so the proposed new method provides an easy and safe method. This ensures heating at constant temperature (150 deg C) so no safety concern about pressure build up inside the Digestion tube. Moreover the proposed equipment i.e., Chemical Oxygen Demand (COD) digester is available in all SAIL plants.
SUMMARY OF THE INVENTION:

The principle object of the present invention is to provide an improved method of measurement of pH of coal slurry to measure the level of weathering / oxidation in incoming coals.

Therefore such as herein described there is provided a method which determines the weathering status of incoming coal or coal stored in piles. The pH values are correlated with hot strength of coke, i.e., CSR. This may help to better utilization of weathered coal. By changing the blend composition the fluctuations in the coke quality because of use of weathered coal in the blend can be minimized.

A method for measurement of pH of coal slurry disclosed herein includes the steps of : providing representative samples of coal slurry of quantity 0.5g in the form of 60 mesh coal; mixing the coal sample with 5ml of distilled water in a digestion tube; placing the mixture of coal and water sample in a Chemical Oxygen Demand (COD) Digester and the said mixture is heated to 150 deg C; conditioning the mixture sample by maintaining it to 1500C for 2 hours; cooling the said mixture indirectly using tap water to room temperature; transferring the mixture sample into a beaker for measurement of pH using probe, wherein the heating system of COD digester ensures the availability of coal water slurry after heating at 150 deg C for 2 hours.

OBJECT OF INVENTION:

It is an object of this invention to provide an easier and safe method to measure pH of coal slurry.

It is another object of this invention to provide an assessment of the weathering status of coal and correlating the pH of coal slurry with coke quality i.e. Coke strength after reaction (CSR).

It is another object of this invention to make changes in the blend composition so that fluctuation in the coke quality can be minimized.

It is another object of this invention to provide more accurate temperature control during heating the coal water slurry.

This invention ensures heating of coal water mixture at 150 deg C for 2 hours and ensures availability of coal water slurry after 2 hours. This system is easily available in all SAIL plants so can be carried out in all plants.

It is another object of this invention to provide an easier and more accurate system to measure the pH of coal slurry to measure oxidation/ weathering of coals.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:

Fig. 1 illustrates a digestion tube in accordance with the present invention;

Fig. 2 illustrates a COD digester in accordance with the present invention.

DETAILED DESCRIPTION:

Coal slurry pH can be used to characterize coals. The pH values of coal slurry depend on the parameters including water/coal ratio, stirring speed, type of stirrer, design of the vessel and the condition of the process. The pH values depend on the type of coal, mixing time for slurry preparation, contact with gas atmosphere, particle size and stirring. Various attempts were made to establish some correlation among power number, Reynolds number, geometry of the vessel and stirrer, physical properties of liquid and particle.

In the present disclosure tests are carried out with various collected representative samples, which were reduced by coning and quartering and then selected samples were ground and screened through 60 mesh screen. The fraction which passes through 60 mesh screen were used to find the pH of coal slurry.

In this study following steps were adopted:
 Initially 0.5 gm (-60 mesh coal) and 5 ml distilled water was taken in a Digestion tube. Digestion tubes are shown in Fig. 1.
 Digestion tube was kept in a Chemical Oxygen Demand (COD) Digester as shown in Fig. 2 and the mixture of coal and water were heated to 150 deg C. When the temperature reached 150 deg C then it changes to new programme of conditioning which will maintain 1500C for 2 hours. After 2 hours machine will automatically stop.
 The Digestion tube is removed and cooled indirectly using tap water.
 The coal slurry was transferred into beaker and its pH was determined using pH probe.
 This heating system ensures the availability of coal water slurry after heating at 150 deg C for 2 hours.

Using the generated data a prediction model was developed to forecast the weathering status of coal received. For this different type of coal being used in coke making plants were weathered and their pH values and other parameters such as Ash, VM, Vitrinite percentages, basic to acid ratio, day of storage, size of coal stored, Mean max reflectance (MMR) of coals were monitored at an interval of approx. 1 month. These values are shown in Table 1. These data were utilized to develop prediction equation for pH using different coal characteristics data. For prediction, multivariable regression analysis was carried out in Minitab 17.

Minitab is a statistics package developed at the Pennsylvania State University by researchers Barbara F. Ryan, Thomas A. Ryan, Jr., and Brian L. Joiner in 1972.

Minitab provides assistance in regression analysis and fits a model with one continuous response (Y) and two to five predictors (X). There are two types of models to choose
Linear: Y(X)= 0+ 1X1+ 2X2+-----------------+ pXp ----------------- [1]
Quadratic: Y(X)= 0+ iXi+ iiXi2+ ijXiXj ---------------------[2]
Where 0 , 1, ii and ij are constant. X1, X2 and Xp are called as predictor or input variable and Y is response variable also called as output variables. In this study Quadratic model (Eq. 2) is used for prediction.
Input variables: Ash, Volatile Matter (VM), Mean Max Reflectance (MMR), Basic to Acid oxides ratio in coal Ash (BAR), Vitrinite % (Vitri), days of storage (Day), mean particle size of coal (Size).
Output variables: pH of coal
Additionally, Minitab 17 examines several factors that are important to obtain a valid regression model. First, the sample must be large enough to provide enough power for the test and to provide enough precision for the estimate of the strength of the relationship between X and Y. Next, it identifies unusual data that may affect the results of the analysis. It also considers the assumption that the error follows a normal distribution and evaluates the impact of non normality on the hypothesis tests of the overall model.

The limitation of Minitab is that it can use only 5 input variables (X) at a time, so various combinations of input variables were considered to get a maximum R square (R sq.) value, as R sq. closer to 1 represents better regression equations. The equation [3] gave the maximum R square (0.967)

The summary reports of regression analysis shows that p value is below 0.001 means relationship between variables are significant. This equation 3 can be used to predict the weathering status of incoming coals.

The prediction equation for pH is as below:
pH of coal slurry = 11.92+0.380*Ash+0.657*Vitri+0.0826*Day-1.805*BAR-0.00529*(Vitri^2)-0.00908*Ash*Vitri-0.001358*Ash*Day-0.001154*Vitri*Day-0.08221*Day*BAR, ----------------------------- [3]
R sq: 96.74
Where
Ash- Ash in coal (%)
VM- Volatile matter of coal (%)
pH- pH of coal slurry
Vitri- Vitrinite in the coal (%)
Day- Time of storage at interval of 1 month
BAR- Basic to acid oxides ratio of coal

Table 1: Change in pH for Coal Samples on Storage

Storage,
Day pH Ash,% VM,% MMR,% BAR Vitrinite,% Size,
mm
1 5.95 28.5 18.7 1.24 0.150 38.9 4.17
30 5.90 26.8 18.7 1.24 0.150 38.8 4.17
60 5.70 26.8 18.7 1.24 0.150 35.2 4.17
90 5.50 26.2 18.7 1.24 0.150 34.1 4.17
120 5.40 26.2 18.7 1.24 0.150 33.8 4.17
150 5.30 26.0 18.7 1.24 0.150 32.5 4.17
1 6.20 9.0 27.2 1.25 0.108 65.0 2.98
30 6.20 9.0 27.2 1.25 0.108 63.4 2.98
60 6.20 9.0 26.0 1.25 0.108 62.1 2.98
90 6.10 9.0 26.0 1.25 0.108 60.0 2.98
120 5.95 9.0 26.9 1.25 0.108 59.2 2.98
150 5.95 9.0 26.9 1.25 0.108 58.2 2.98
1 6.20 33.0 25.4 0.90 0.160 30.3 6.10
30 6.10 33.0 25.4 0.90 0.160 30.1 6.10
60 5.94 33.0 25.4 0.90 0.160 29.0 6.10
90 5.40 33.0 24.3 0.90 0.160 28.8 6.10
120 5.20 33.0 24.3 0.90 0.160 27.8 6.10
150 5.10 33.0 24.3 0.90 0.160 27.4 6.10
1 6.10 8.4 26.0 1.11 0.312 64.4 2.81
30 5.70 8.4 26.0 1.11 0.312 63.3 2.81
60 5.26 8.4 25.1 1.11 0.312 61.4 2.81
90 3.86 8.4 25.0 1.11 0.312 60.8 2.81
120 3.50 8.2 25.0 1.11 0.312 59.9 2.81
150 3.40 8.2 24.9 1.11 0.312 58.5 2.81
1 6.70 9.2 25.0 1.02 0.270 53.9 2.79
30 6.20 9.2 25.0 1.02 0.270 52.4 2.79
60 5.80 9.2 25.0 1.02 0.270 51.4 2.79
90 5.51 9.2 24.5 1.02 0.270 50.9 2.79
120 5.40 9.2 24.5 1.02 0.270 49.8 2.79
150 5.30 9.2 24.3 1.02 0.270 48.7 2.79

Many coke plants and blast furnaces around the world use CSR as a specification just as important as cold strength, size, and chemistry. Researchers have studied reactivity and its influence on blast furnace performance and productivity. The use of both physical and mathematical models of the various blast furnace zones, the monitoring and sampling of heavily-instrumented blast furnaces, and the quenching and subsequent sampling of commercial furnaces have aided in determining the effect of changes in coke reactivity on furnace operating parameters such as fuel rate, furnace permeability, and hot metal production. Further, pH values are correlated with hot strength of coke i.e. CSR. For this coals were weathered in open piles and coke was made by using box charging in commercial oven. Some of these data are shown in Table 2.

Using these data Multivariable linear regression model was developed. MS EXCEL 2007 was used for Mmultivariable linear regression analysis, using the data generated (Table 2). In this study it was attempted to develop regression equation which include weathering indicators, to assess the impact of weathering on coke quality. For this:
Input variables: Ash, Volatile Matter (VM), Vitrinite % (Vitri), MMR, FSI, pH Output variables: CSR (Coke Strength after reaction)

The regression equation Eq. [4] correlates the pH value of coal slurry with CSR. The developed equation helps to predict the effect of change in pH value with respect to CSR. This may help to change the blend accordingly to minimize the effect of weathering on the coke quality.

It is well known that increase in CSR have led to decreases in blast furnace fuel rates. The magnitude of fuel rate reductions varies for different blast furnaces and operating parameters. The exact effect of coke reactivity on blast furnace performance is not completely clear; however, most furnace operators agree that the coke should not readily react at lower temperatures in the upper zone of the furnace to avoid wasted carbon. Also, highly reactive coke may become substantially weakened so that it cannot properly support the burden during its descent through the blast furnace. By the time the coke works its way to the high temperature combustion zone, or raceway, the coke may become so weak that it causes major upsets to occur in raceway performance. Poor raceway behavior restricts both gas and liquid permeability in the blast furnace, reducing overall furnace efficiency.

CSR = (-206.60-5.59*Vitrinite-25.92*Ash+29.79*pH+27.04*VM) -- [4]
R Square=0.97
Where:
VM- Volatile matter of coal (%)
pH- pH of coal slurry
Vitrinite- Vitrinite in the coal (%)
Ash- Ash in coal (%)

Table 2: Change in CSR for coal sample on storage

Storage,
Day Vitrinite% Ash VM pH CSR
1 65.0 8.9 25.0 6.10 61.1
60 62.1 8.3 24.0 6.05 57.6
1 65.0 9.0 24.0 7.00 51.2
60 62.2 9.0 23.0 6.95 43.7
1 64.4 9.2 25.6 4.65 22.4
60 61.4 8.8 25.5 3.65 21.8
1 85.0 6.7 27.5 5.10 40.4
60 84.6 6.7 27.0 4.95 23.8

Inventive step

The proposed innovative method invented during a project at Bhilai Steel Plant. In this study a simple method was developed to measure the pH of coal slurry. This can be used to identify weathered coal and its level of weathering based on the pH value. A prediction model was also developed which can forecast the pH value after certain period. This can help in deciding the limiting storage period of weathered coal.

A large number of data were generated at BSP to correlate the pH of coal slurry with hot strength of coke. It helped in understanding the weathering impact on coke quality. By knowing the weathering status of coal and expected coke quality, fluctuation can be minimized by properly changing the blend compositions.

The proposed method helps in identification of the weathering status of incoming coals. At present weathered coals are identified by changes in FSI, change in fluidity but measurement of pH of coal slurry is not in practice. The proposed method can be easily implemented in all Steel Plants. This will help in identification of weathering coal and fluctuations of coke quality can be minimized.

Although the foregoing description of the present invention has been shown and described with reference to particular embodiments and applications thereof, it has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the particular embodiments and applications disclosed. It will be apparent to those having ordinary skill in the art that a number of changes, modifications, variations, or alterations to the invention as described herein may be made, none of which depart from the spirit or scope of the present invention. The particular embodiments and applications were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such changes, modifications, variations, and alterations should therefore be seen as being within the scope of the present invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.