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Key words: Texaco; gasifier; coal water slurry; sensor; electromagnetic flowmeter; AC excitation converter; electrode Introduction With the continuous development of coal chemical projects in China, Texaco gasifier coal slurry flowmeter Application is more and more extensive. The two methanol projects that are used as the background of this article have adopted the Texaco gasifier process. The coal slurry concentration is about 62% (wt/wt), the average particle size is about 31μm, the pipeline is DN150, the pressure class is 600lbs, and the production capacity is 200000t. However, since the start of production, the original imported flowmeters have not been satisfactorily operated and frequently fluctuate. Vertical tube flowmeters fluctuate more frequently, and sometimes crossflowmeters fluctuate together. This can easily lead to miscarriage and bring great losses to the company. It also significantly increases the labor intensity of related departments.
In view of the problem of tripping accidents due to fluctuations in coal slurry flowmeters, the causes of fluctuations in coal slurry flowmeters were analyzed. Special structural sensors and new-generation AC excitation converters produced by Shanghai Welltech were used to effectively prevent The jumping accident caused by the fluctuation has achieved the expected application effect.
1 Analysis of Causes of Fluctuations According to the principle of electromagnetic flowmeters, relevant literature, and long-term application experience, the root cause of flow field fluctuations depends on the flow field and flow state of the fluid in the electromagnetic flowmeter measuring tube [1]. The corresponding relationship between the flow and flow rate of DN150 measuring tube is shown in Table 1. In normal production, the flow rate is generally about 25m3/h, and the corresponding flow rate is only 0.4m/s. The fluid velocity is low, and the concentration of coal slurry is as high as more than 60%. This easily leads to the unsteady flow field in the pipeline, and the unsteady state of the vertical tube and the horizontal tube is different [2]. 
In Fig. 2, the weight of the center point is 1. The weight function distribution of the electrode plane is given. From Figure 2, we can see that the closer to the electrode, the greater the weight; the other hand, along the catheter 90 °, the minimum weight.
The two distributions of the coal slurry flow velocity in the electrode plane are shown in FIG. 3, and the distribution of the weight function is the same as in FIG. 2. 
The ideal flow field distribution should be axisymmetric. The center is slightly larger and the circumference is slightly slower. At this time, the flow rate measured by the electromagnetic flowmeter is accurate and stable (except for the influence of slurry noise). If the flow field is not ideal, the uneven distribution of the flow velocity in the cross section of the measuring tube may cause fluctuations in the flow measurement output.
From Fig. 3(a), it can be seen that where the weight function is high, the flow rate is fast, and where the weight function is low, the flow rate is slow. At this time, the converter flow output increases. From Fig. 3(b), it can be seen that the flow rate is fast at the place where the weight function is low. Whereas, where the weights are high, the flow rate is slow and even the electrodes are covered. At this time, the output of the converter is reduced, even close to zero.
The reason for the fluctuation of the horizontal tube is different from the above analysis. The fluctuation is mainly caused by siltation. If the deposition surface does not exceed the electrode, the output of the converter will increase as the cross section of the measuring tube decreases and the flow rate increases. If the deposition surface exceeds the electrode, the converter output will decrease. Since this siltation is unstable and the deposition surface is up and disappearing, it causes a long fluctuation of the flow output period. Generally speaking, in the initial stage of feeding, the horizontal tube performs better. After a period of time, the horizontal tube will fluctuate.
2 Solution Prior to this, most people believed that the flow meter fluctuates due to slurry noise and even electrode noise. Since the cycles of slurry noise and electrode noise are relatively short, the method of processing fluctuations is nothing more than to increase the damping time. Facts have proved that this method cannot fundamentally solve the problem of skipping caused by fluctuations in the flowmeter output.
After the above analysis, we believe that the root cause of flow meter output fluctuations is the flow field flow state, which is characterized by a relatively long fluctuation cycle, the cycle is a few seconds or even tens of seconds. To improve the flow field flow, we need to start from the sensor structure design. Therefore, a venturi-shaped sensor is used, which not only increases the flow velocity but also provides a certain degree of rectification. Application experience shows that when the flow rate is about 1m/s, the flow field is relatively good. To eliminate abnormal fluctuations of large and long periods, the sensor thus designed plays a key role.
In order to solve the abnormal fluctuation of the flowmeter, it is not enough to change the structure of the sensor alone. Because the original imported electromagnetic flowmeter is square wave excitation, the use of so-called low-noise electrodes and higher-priced ETFE linings cannot effectively solve the converter's problem of conquering slurry noise. In addition, the slurry noise increases with the flow rate. After the diameter reduction, if a square-wave excitation converter is used, fluctuations in the long-period cycle can be avoided, but the problem of fluctuation in the fast cycle cannot be solved. What's more serious is that this kind of fluctuation may also lead to jumps.
In order to make the converter output smooth, the use of square wave excitation converter can only increase the damping time. However, the Texaco gasifier's safety interlock scheme imposes stringent restrictions on the meter's damping time. According to professional estimates, if the coal slurry pipeline is plugged, the oxygen cutoff time is only 8 to 10 seconds. If the flowmeter is damped too long, there is a danger of peroxygen explosion.
From the above analysis, we know that Texaco's process requires that the coal slurry flowmeter output is not only smooth (to prevent false trips), but also that the reaction speed is fast (once the pulp is broken, the safety interlock is quickly activated, oxygen is cut off, and the burner brick is prevented from burning or peroxidation. explosion). Since the square wave excitation electromagnetic flowmeter has its own defects in measuring the slurry, an AC excitation converter should be used. The new generation of AC excitation converters produced by Shanghai Weltech, due to the use of high-order band-pass filters, can achieve stable and fast flow measurement output. In our actual project, we have used a damping time of 0.2s to run safely and reliably for more than two years.
Because the causes of cross-tube fluctuations are different from those of standpipes, the processing methods are also different. In China, electromagnetic flowmeter manufacturers used to model a Welsh's standpipe flowmeter to reduce the diameter and apply it to a horizontal pipe. The effect of actual use is not ideal. The horizontal tube solution provided by Welcht is shown in Figure 4. 
From Fig. 4, it can be seen that the measuring tube of the flowmeter is in the shape of a half moon, and the upper half is blocked. This is mainly to prevent blockage of the pipeline caused by the lower closure. In order to improve the flow field, deflectors are also designed upstream and downstream of the flow meter. The converter still uses the second-generation AC excitation technology.
3 Application effects The solution proposed in this paper has been successfully applied to two domestic coal chemical companies. First, the solution was applied to a standpipe that fluctuates relatively frequently. The cross pipe still uses the original inlet flowmeter. An enterprise has caused tripping accidents up to tens of times a year because of frequent fluctuations in the original imported flowmeter. Because the stability of the coal slurry flow meter provided by Welltech is much better than that of other similar products, the company has never caused erroneous jumps due to fluctuations in the flowmeter since it was put into operation. Figure 5 shows the comparison of the flow output stability obtained from the screenshot of the monitoring system workstation. As can be seen from Figure 5, when the inlet flow meter located in the horizontal tube fluctuates greatly, the output of the vertical tube Weltay flowmeter remains stable. At the same time, the craftsman used the furnace temperature and other parameters to make a comprehensive judgment, which also proved the stability of the standpipe flowmeter output. 
Weltech coal slurry flowmeters have now been operating reliably for more than three years, and they have not lost their imports during the service life.
The cross tube solution was researched and tried after the standpipe was successfully applied. The original inlet flowmeter installed on the horizontal pipe generally starts to fluctuate within a week or so. The flowmeter of Voltaire reached a steady state in about 8 hours, and the flow output was very stable at the beginning. After about 8 hours, the fluctuation became slightly larger, but there was no significant fluctuation. After more than half a year of use, at present, the cross tube solution has passed the acceptance and the effect is better than the original imported flow meter. However, the installation of the flow meter guide plate is more complicated. Welch has improved the design and the new program will be put into trial operation.
4 Misunderstandings In practical applications, the application of electromagnetic flowmeters in Texaco process water-coal slurries often has some misunderstandings in the selection and application of relevant technicians [7-8]. It is summarized as follows.
1 "The wear of the coal slurry is large, so the wear-resistant ETFE lining" is inaccurate, and ETFE mainly solves the problem of adhesion to the metal. Although ETFE's raw materials are cheap, its current treatment process is complex, and its use to make linings is more costly than PFA, and there is no evidence that ETFE's wear resistance is superior to that of PTFE. Sensors produced by Shanghai Weltech use hard rubber linings and have been effectively used on site for three years without noticeable wear.
2 "The use of low-noise electrodes, so the small fluctuations" is not accurate. The shape of the electrode does correlate with the size of the noise. Because the electrode of the original imported flowmeter has fouling phenomenon in a coal chemical enterprise, it is often necessary to remove the flowmeter to grind the electrode with crystal phase sandpaper, and Shanghai Weltech uses a self-cleaning electrode (ie, a sharp electrode) to effectively solve the problem. Scale problem. The practical application shows that although the smoothness of the self-cleaning electrode meter is slightly worse than that of the spherical electrode, there has been no abnormal fluctuation. Therefore, we believe that low-noise electrodes are not a key technology in solving the abnormal fluctuations in the flow output of coal paddles.
3 "The original import flow meter installation requirements are low, '2D' after the first 5D on the line' is not accurate. In the laboratory calibration, the straight pipe section is required to be long (up to 10D); in the application, the general "3D after the first 5D" is sufficient, which is not only applicable to the inlet flowmeter. If the diameter is reduced, the straight pipe section requirement can be further reduced. In addition, at this stage, the coal slurry flowmeter basically does not have closed-loop control, and the requirements for accuracy are not very high. The key is to ensure that the safety chain is in an effective state to avoid the abnormal fluctuations that cause false tripping.
4 "The original imported flowmeter flow rate has little effect on the flow, the application of flow rate of 0.3m/s" is not accurate. This statement is very misleading. Practical application experience shows that when the flow rate is low, especially when the flow rate is lower than 0.5m/s, the coal slurry flowmeter fluctuates easily. Therefore, this view is inaccurate.
5 The concept of "simple diameter reduction" is inaccurate. We have modeled the diameter reduction of Shanghai Weltech's shrinkage scheme and installed a smaller diameter flowmeter. However, the actual results are not as good as those proposed in this paper. On the one hand, due to the transformation of pipelines, high-pressure flanges and pressure vessel-level welding, the overall cost is not low; on the other hand, the diameter of the pipe is reduced, and the small-diameter length is much larger than the diameter of the flowmeter, resulting in increased pressure loss. Large, plus the converter is not replaced, many of the results are unpredictable.
The viewpoint that "the original imported flowmeter has a large number of performances and therefore a small risk" is inaccurate. There are two concepts of high performance and good performance. There is no causal link between the two. Due to historical reasons, the market share of original imported flowmeters was relatively high. Although there were many good results, there were also poor results. Once the fluctuations cause false trips, the loss is great. According to incomplete statistics, because the coal slurry flow meter caused a false jump, a loss of 200,000 tons of methanol production line is about 300,000 yuan; 600,000 tons of methanol production line, the loss of a wrong trip once about 800,000 yuan. This is also one of the reasons why the price of high-quality slurry flow meters is high. We have used two brands of imported flowmeters. Eight months have seen bad conditions and three bad cases in one year. The solution provided by Shanghai Weltech has carried out a number of targeted designs for the specific conditions of the Texaco gasifier site. It has now been used safely and reliably for more than three years.
In summary, we believe that the right choice is the best choice for practical application. In the measurement of coal slurry flow in Texaco gasifier, the fluid parameters involved in flow field flow are more complex, and the source of coal and the formula of coal slurry are not the same. Therefore, the application effect of different coal slurry flowmeters is also quite different. The same kind of flow meter is prone to fluctuate in some occasions, but it has good application effect in other occasions, which is caused by the lack of a stable working range of the selected coal slurry flow meter.
In order to minimize or avoid false tripping and ensure that the safety chain is in an effective state, a slurry flow meter with a wider range of stable operation should be selected, and selecting a slurry flow meter that is stable and fast is a basic requirement for the process.
5 Conclusion Since the measurement of coal-water slurry flow is a difficult area in the Texaco process coal chemical industry, colleagues in this field have made a lot of work and efforts to actively seek effective solutions.
In this paper, two Texaco gasifier processes are used as the background, and the volatility of the coal slurry flowmeter indications is relatively large, resulting in two important interlocking of oxygen-coal ratio and coal slurry flow can not be effectively invested, thus becoming a coal chemical industry. The biggest security risk in production. In order to solve this problem, the author has analyzed in detail the misunderstandings of the current field of coal slurry flow meter application, put forward his own unique views and views, and further improved the measurement method of coal water slurry flow in the Texaco process coal chemical industry [9 -11].
This article has received guidance and help from Dr. Zhang Zhenshan. I am deeply grateful for this.
References [1] Wang Qiufen, Chen Liangyong, Ren Yuan, et al. Rheological characteristics and slip correction of high-concentration coal water slurry[C]//The Chinese Society for Engineering Thermophysics Multiphase Flow, 2006:446-453.
[2] Ji Gang. Flow measurement instrument application skills [M]. Beijing: Chemical Industry Press, 2008: 114.
[3] Huang Baosen, Kong Zhaoyu, Jing Yongfang, et al. Electromagnetic flowmeter [M]. Beijing: Atomic Energy Press, 1981:22-25.
[4] Cai Wuchang, Ma Zhongyuan, Ruan Guofang, et al. Electromagnetic flowmeter [M]. Beijing: Sinopec Press, 2004: 25-72.
[5] Cai Wuchang, Ying Qichen. New type flow detection instrument [M]. Beijing: Chemical Industry Press, 2007:33-34.
[6] Zhang Xiaozhang. The theory and method of flowing electromagnetic induction measurement[M]. Beijing: Tsinghua University Press, 2010:17-24.
[7] Si Yuan. Type selection of coal slurry flow meter[J]. Process Industry, 2009, 21(12):48-49.
[8]Syuan.Application of electromagnetic flowmeter in Texaco gasifier[J].Heilongjiang Science and Technology Information,2009,36(12):80.
[9] Chen Jinxing. Application of ADMAGA electromagnetic flowmeter in the measurement of coal water slurry[J]. Petrochemical Automation, 2002, 75(12): 75-77.
[10]WANG Yongzhou.Application experience of slurry electromagnetic flowmeter in coal chemical industry[J].Coal Mine Modernization,2010,95(2):91-92.
[11] Ni Xinglai, Xue Lingfei. Research and Application of Slurry Magnetic Flowmeter in Coal Chemical Industry Coal Water Slurry Industry[J]. China Instrumentation, 2010, 232(12): 53-55.
Application of Coal Slurry Flowmeter in Texaco Gasification Furnace
Abstract: With the continuous development of coal chemical projects in China, Texaco gasifier coal slurry flowmeter has been more and more widely used. In view of the problem of tripping accident caused by the fluctuation of coal slurry flow meter, the cause of fluctuation of coal slurry flowmeter was analyzed. Taking the domestic two 200000t methanol projects in the background of the problems encountered in the application of coal slurry flowmeters, a special structure of sensors and a new generation of AC excitation converters were adopted, and good practical application results were achieved. Finally, according to the actual application experience, according to the misunderstanding of the current application field of coal slurry flowmeter, put forward their own opinions and views. In the standpipe, the flow velocity in the center is relatively fast, and the surrounding flow rate is relatively slow, which makes the surface of the tube wall adhere to a layer of coal slurry that flows very slowly. If the adhesion layer is slow and hardly moving and it is thick, it covers the electrodes and the converter's flow output will drop, even to zero. Because the working mode of the coal slurry pump is pulsating, the coal slurry pipeline is also vibrating, and because the vertical pipe is very high, the coal slurry attached to the inner pipe wall is in an unstable state, and the avalanche phenomenon may occur from time to time in the pipeline. And this avalanche phenomenon is not necessarily one. Coal slurry flow state diagram shown in Figure 1. If this avalanche occurs in the measuring tube of the flow meter, it will cause the output of the converter to fluctuate. The period of output fluctuation caused by "avalanche" is faster and the damping time is increased, which can play a certain role in smoothing.
Fig.1 Schematic diagram of coal slurry flow
In the production process, the most difficult to deal with is another kind of fluctuation. The cycle of this fluctuation is very slow, but it is large enough to cause a jump. To explain this phenomenon clearly, we need to introduce the concept of weight function [3-6]. Roughly speaking, the weight function gives the contribution rate of the induced electromotive force generated by fluid cutting magnetic lines at different positions to the electrode signal. The weight function diagram is shown in Figure 2. Figure 2 Weight Function Schematic
Fig. 3 Schematic diagram of uneven flow velocity distribution
Figure 4 Horizontal tube fluctuation solution
Fig. 5 Comparison of traffic output stability
In order to accurately compare the rapidity of output of different electromagnetic flowmeters, two electromagnetic flowmeters were installed in the same pipeline for testing. The horizontal tube was an inlet flowmeter and the standpipe was a Weltern flowmeter. During the test, the coal slurry pump was suddenly shut off, turned on again at a time, and the coal slurry pump speed was gradually increased. Figure 6 shows the current output results of two electromagnetic flowmeters recorded at the same time and captured by the DI-730 data collector. The horizontal coordinate of each cell in Figure 6 is 3s. It can be seen from Fig. 6 that the total time of the zero flow from the broken pulp to the flow output of the Weltay flowmeter is about 6s, and the filtering time constant can be estimated to be less than 2s from the falling process, completely satisfying the safety interlock requirement; The inlet flowmeter has a reaction time of more than 30 seconds. Figure 6 Comparison of the rapidity of flow output
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