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Pressure Characteristics of Multiple-Tube Ceramic Filter Pulse Cleaning System [Sensors & Transducers (Canada)](Sensors & Transducers (Canada) Via Acquire Media NewsEdge) Abstract: The dynamic pressure characteristics of pulse jet pipe, pulse jet nozzles and ceramic filter can be measured by high-frequency dynamic pressure sensor. The research is focused on the influence of cleaning pressure, the diameter of nozzles, and the ratio of sectional area of nozzles to that of pulse jet pipe on pulse cleaning performance. The results show that the difference of pulse jet nozzles performance increases when cleaning pressure increases. The main reason leading to the difference of pulse cleaning is that the increasing rate of static pressure along cleaning direction is slow after the first large increase. The diameter of pulse jet nozzles has a significance affect on cleaning performance so that the uneven performance can be improved by decreasing the diameter of nozzle along the cleaning direction ladder likely. The ratio of sectional area of nozzles to that of the pulse jet pipe is a key factor in cleaning performance, and the best range of the ratio of sectional area of nozzles to that of the pulse jet pipe in the research is from 45 % to 55 %. Copyright © 2014 IFSA Publishing, S. L. Keywords: Pressure sensor, Pulse cleaning, Ceramic filter, Dynamic pressure, Data acquisition system. 1. Introduction Hot gas filtration from industrial processes offers various advantages in terms of improvement of process efficiencies, heat recovery and protection of plant installation. Especially, hot gas filtration is an essential technology for pressurized fluidized bed combustion (PFBC) and integrated gasification combined cycle (IGCC), promising coal fired generation of electricity with substantially greater thermodynamic efficiencies and reduced particulate pollutant emissions [1-4]. The filtration protects gas turbine blades from the erosion and corrosion and improves the performance of a heat exchanger connected to a steam turbine by decreasing particles deposition [5,6]. Because the high-temperature ceramic filter has the following advantages such as compact structure arrangement, corrosion resistance and thermal shock resistance, dust particles bigger than 5 pm can be removed. The outlet dust concentration is less than 5 mg/Nm3 and the separation efficiency is more than 99.9 %. It is recognized as the most promising high-temperature gas dust removal technology [7, 8]. Uneven pulse cleaning is a common problem during actually operation, which affects the stability of hot gas filtration operation [9-11]. Scholars research in the pulse cleaning system performance usually by using method of numerical simulation and flow calculation [12-14]. Because there is instantaneous flow velocity during pulse cleaning, it is more difficult to measure the pressure and velocity of the pulse jet nozzles, and the pulse cleaning system parameters is determined empirically. Experimental study mainly focuses on the pulse cleaning system with a single nozzle. In this article, high-frequency dynamic pressure sensor is used for analyzing the pressure characteristics of multipletube ceramic filter pulse cleaning system, which has 12 ceramic candle filters inside the filter vessel. Pulse cleaning pressure, nozzle diameter and the ratio of sectional area of nozzles to that of the pulse jet pipe are tested in order to provide guidance for the development of efficient determinant pulse cleaning technology. 2. Experiment and Method Fig. 1 is the experimental set-up schematic diagram of pulse cleaning system. The volume of pressure air tank is 0.3 m3. P is the pressure measurement point, and the pressure decreasing value is less than 10 % of the original pressure value during pulse cleaning. Australia GOYEN RCA40T mode solenoid valve is selected as the pulse cleaning valve. The pulse jet pipe length is 1500 mm, the inner diameter of the pipe is 42 mm. There are 5 pressure measuring points on the upper wall of the pulse jet pipe, which are A, B, C, D and E respectively. The adjacent central distance of measuring point is 185 mm. There are 12 pulse jet holes at the lower part of the pipe, and the position of the pulse jet holes (PI-PI2) are distributed along the direction of the pipe. The central distance of adjacent pulse jet holes is 100 mm, and nozzles with the diameter of 7, 8, 9, 10 and 12 mm can be mounted on these holes. Each nozzle is connected to a cylinder, of which the inner diameter of the cylinder is 40 mm and the height of the cylinder is 150 mm. Pressure sensor for measuring the pressure characteristics of the nozzle outlet is installed at the central position at the bottom of the cylinder. Germany Schumacher product mode DS10-20 porous ceramic filter candle is used for the research. The filter porosity is about 37 %, the length is 1500 mm, the outer diameter is 60 mm and the inner diameter is 40 mm. Pressure sensors are installed along the axial outer wall of the filter candle. Since the pressure range of the pulse jet pipe, the pulse nozzles and the filter candle are different to each other, it is necessary to use different range of pressure sensors to measure the high-frequency transient dynamic pressure during pulse cleaning. 050 kPa (model CGY202) and 0-500 kPa (model CGY208) pressure sensors are chosen for the research. The measurement accuracy of the pressure sensor is ± 0.25 % of the pressure range, and the natural frequency of the pressure sensor is greater than 50 kHz. In order to avoid the effect of the lumen, the probe position of the pressure sensor is flush with the measuring points. Data acquisition system includes industrial control computer (Advantech IPC-510), PLC controller (SIEMENS EM231) and data acquisition card (Altai PCI8622). PLC controls the signal acquisition and triggers the pulse duration of solenoid valve. It can be showed from the results that bigger pulse duration increases cleaning gas consumption. However, bigger pulse duration has little effect on improving the pulse cleaning performance [15], so smaller pulse duration of 250 ms is set during the test. While pulse cleaning gas is injected into filter candles, pressure signal is converted to an electrical signal by pressure sensors, and the signal is transmitted to a computer for processing. The data acquisition card has 32 parallel channels with the accuracy around 500 kHz, which can meet the rapid data acquisition requirements. 3. Results and Discussion 3.1. The Pressure Analysis of Pulse Jet Pipe, Pulse Jet Nozzles and Filter Candle Fig. 2 shows the variation of pressure wave at points A, C and E. The cleaning pressure is 0.5 MPa, and the pulse jet nozzles diameter is 9 mm. During pulse cleaning process, the pressure inside the pulse jet pipe increases rapidly to the maximum value. The reason for this phenomenon is that while the solenoid valve is opened rapidly, the compressed gas is released instantaneously, and the energy of the high velocity gas inside the pulse jet pipe mainly performs as dynamic pressure. As the pulse jet gas flow ejected from each nozzle quickly, the pressure inside pulse jet pipe decreases rapidly, resulting in the biggest pressure inside the pipe. The pressure wave's variation is similar to each other and the only difference is the pressure peak value, which is selected for determining pressure characteristics. Fig. 3 shows the variation of pressure wave at points P3, P7 and PI 1. The cleaning pressure is 0.5 MPa and pulse jet nozzles diameter is 9 mm. As a result of the impact of high-speed air to the probe nozzle diaphragm of the pressure sensor, the pressure propagation goes back and forth, causing the nozzles outlet pressure fluctuation. The diameter of the diaphragm is 1.5 mm and the pressure sensor diaphragm probe is in the free jet region. The measurement results reflect the energy of the pulse cleaning. Measurement results show that the pressure value gradually increases at the points P3, P7, and PI 1, indicating the cleaning intensity increases along pulse cleaning gas flow direction. Fig. 4 shows the pressure wave's variation along the axial of the filter candle. The cleaning pressure is 0.5 MPa and pulse jet nozzles diameter is 9 mm. It can be seen from the figure that the pressure value of top, middle and bottom position gradually increases. While the pulse cleaning gas injects into the filter candle, the gas flow velocity decreases along axial direction of filter candle, causing the static pressure increases, and therefore the pressure value of top, middle and bottom positions is increased successively. 3.2. Effect of the Pulse Cleaning Pressure Fig. 5 shows the pressure value variation along the pulse jet pipe. The cleaning pressure is 0.5 MPa and pulse jet nozzles diameter is 9 mm. The figure shows that the pressure peak of the pulse jet pipe increases with increasing pulse cleaning pressure. With the higher pulse cleaning pressure, the distribution inside the pulse jet pipe is more uneven. While the pulse cleaning pressure value is 0.2 MPa and 0.6 MPa, the pressure value of A and E is about 2 kPa and 14 kPa, respectively. Because pulse cleaning gas constantly ejects from the nozzles, there is a critical position which causes the pressure inside the pulse jet pipe firstly increasing and then decreasing. Fig. 6 shows the pressure value variation of pulse jet nozzles at different cleaning pressure. The pulse jet nozzles diameter is 9 mm. The pressure peak increases along the direction of cleaning gas flow direction. The pressure peak is bigger with bigger pulse cleaning pressure. While pulse cleaning pressure is 0.2 MPa and 0.6 MPa, the differences of pressure peak value between PI and P12 are 30 % and 70 %, respectively. 3.3. Effect of pulse jet nozzle diameter Fig. 7 shows the pressure variation of pulse jet pipe with different diameter nozzles. Results show that pressure variations of pulse jet pipe are substantially the same to each other. The static pressure gradually increases along the cleaning gas flow direction, but the rate of pressure increases faster at first and then gradually decreases. The pressure increasing rate of between A and C is greater than that after point C. The results agree well with the measurement results in Fig. 5. While using pulse jet nozzles with larger diameter, it is found that the gas consumption is more than that of using smaller diameter of pulse jet nozzles. This phenomenon results from a lower static pressure inside the pulse jet pipe. Fig. 8 shows the pressure variation of different pulse jet nozzles. The pulse cleaning pressure is 0.5 MPa. It is found that as the nozzles diameter increasing, the pressure peak of the nozzles decreases gradually. A pressure peak difference of 18 kPa can be found by using the 8 mm and 12 mm diameter nozzle, respectively. There is pressure fluctuation using 7 mm diameter nozzles. The reason for this phenomenon is that small diameter nozzle is likely to cause greater static pressure inside the pulse jet pipe, so that pulse cleaning gas can not be successfully ejected from the nozzles. Fig. 9 shows the pressure variation at the bottom of filter candle with different diameter nozzles. The pulse cleaning pressure is 0.5 MPa. It is found that the pressure peak decreases as the diameter of nozzles increases. The 8 mm diameter nozzle presents a better performance during pulse cleaning. The pressure peak increases gradually, and then decreases to some extent finally. The pulse cleaning gas flow rate of nozzles increases along the pulse cleaning gas flow direction, but it decreases after a critical position, which is point P9 in this test. 3.4. Effect of the Ratio of Sectional Area of Nozzles to that of Pulse Jet Pipe The pulse cleaning differences can be balanced to some extent by changing the diameter of nozzles. The research based on 5 kinds of diameter of nozzles and 12 kinds of combinations arrangement are tested so as to investigate effect of the ratio of sectional area of nozzles to that of pulse jet pipe. Fig. 10 shows the pressure value inside filter candle of at different arrangement, s represents the sectional area of nozzles and S represents the sectional area of pulse jet pipe. It can be seen from Fig. 10(a) and Fig. 10(c) that there are differences between different nozzles during pulse cleaning. The s/S in Fig. 10(a) is in the range of 0.38-0.44, and there is no obvious rule in the result. The s/S in Fig. 10(c) is in the range of 0.57-0.69, and results show that the pressure peak presents a decline trend. The s/S in Fig. 10(b) is in the range 0.45-0.56, and it is found that the pressure peak values are quite closed to each other. While the s/S value is too small, it is likely to result a larger static pressure inside the pulse jet pipe, and this phenomenon finally results in an unstable pulse cleaning performance. On the contrary side, if the s/S value is too big, it will consume more cleaning gas. In this study, the preferred value of s/S is in the range of 45 % to 55 %. 4. Conclusions The difference of pulse jet nozzles performance increases when cleaning pressure increases. The increasing rate of static pressure along cleaning direction is slow after the first big rate. There is appropriate range for different nozzle diameters. The smaller nozzles (8 mm in this test) can generate higher pressure peak inside the filter candle, which is beneficial to enhance the pulse cleaning performance. However, if the nozzle diameter is too small (7 mm in this test) will result in poor stability pulse cleaning. The diameter of pulse jet nozzles has a significance affect on cleaning performance so that the uneven performance can be improved by decreasing the diameter of nozzle along the cleaning direction ladder likely. The ratio of sectional area of nozzles to that of the pulse jet pipe is a key factor. In this study, the preferred value of s/S is in the range of 45 % to 55 %. References [1]. S. S. Xu, Research on optimizing structure and parameters of the moving granular bed filter for high temperature dust removal in IGCC and PFBC systems, Proceedings of the CSEE, Vol. 5, Issue 19, 1999, pp. 13-17. [2]. H. Steffen, Hot gas filtration - A review, Fuel, Vol. 142, Issue 2,2013, pp. 83-94. [3]. S. D. Sharma, M. Dolan, A. Y. 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Shi, Influence of operating parameters on pulse cleaning process of ceramic filter, Journal of Chemical Industry and Engineering (China), Vol. 55, Issue 7, 2004, pp. 1156-1160. 1 Liang YANG,1 Zhongli JI,2 Tong LAI 1 College of Mechanical and Transportation Engineering, China University of Petroleum, Beijing, 102249, China 2 College of Chemical Engineering, China University of Petroleum, Beijing, 102249, China 1 Tel: +86-10-89734336, fax: +86-10-89734336 1 E-mail: [email protected] Received: 8 June 2014 /Accepted: 27 June 2014 /Published: 30 June 2014 (c) 2014 IFSA Publishing, S.L. |