Application of Three New Flowmeters in Acetic Acid Plant
Mining Machinery Engineering is an interdisciplinary branch of engineering that applies the principles of mechanical engineering, electrical engineering and mining engineering for analysis, design, manufacturing and maintenance of mining equipment. It includes study of various aspects of equipment used in earthworks, mineral processing, bulk material handling, drilling and construction. Coal Mining Machinery,Metal Ore Machinery,Roadheader Equipment,Roadheader Machinery NORTH HEAVY GRYPS EQUIPMENT AND ENGINEERING CO.,LTD , https://www.nhgtunnel.com
The synthesis of acetic acid by low-pressure methanol carbonyl is based on carbon monoxide and methanol, carbonyl ruthenium as the main catalyst, hydroiodic acid and methyl iodide as cocatalysts, crude acetic acid is synthesized at 190° C. and 2.8 MPa, and then flashed, separated and purified. Pure acetic acid product is the most advanced acetic acid production process at present. The use of this technology for the production of acetic acid in China has continued to build and is in a stage of rapid development. This process is characterized by high temperature, strong corrosion, corrosive media in addition to a variety of concentrations and temperatures of acetic acid, as well as hydrogen iodide, iodine methane and other extremely corrosive media, the corrosive environment is complex.
With the continuous progress of the flow measurement technology, the original acetic acid device, such as the orifice plate, vortex street, turbine, oval gear, etc., are easily worn out, corroded and leaked by the medium, the service life is short, and the maintenance workload is large. In the technical reform, according to the process requirements and the characteristics of different media, a variety of new flowmeters were used instead of the originally designed flowmeters. Good results were achieved in the production practice, which not only met the process requirements but also significantly reduced the investment and maintenance strength. The following briefly introduces the use of the three types of flowmeters.
1 integrated T-type Annubar flowmeter 1.1 Annubar flowmeter characteristics Annubar flowmeter is based on the principle of Bernoulli energy conservation and pitot tube measuring principle and developed differential pressure equal-speed tube flowmeter. It has undergone three stages of development: the first generation of circular annubar, the test rod section is circular; the second generation of gem I, the detection rod section is diamond, the second generation of improved gem type II, detection rod section is Improved diamond; 3rd generation T-type Annubar, measuring rod section is T type.
T-type Annubar flowmeter has excellent intrinsic anti-blocking performance, high accuracy and stability, outstanding signal-to-noise ratio and range ratio, integrated installation of temperature and pressure compensation, and convenient installation.
The Annubar flowmeter can measure the volume flow or mass flow of the medium. The combination of the T-type Annubar and the multi-parameter transmitter can measure the mass flow of the medium. The multi-parameter transmitter has a built-in high-precision differential pressure transmitter. , absolute pressure transmitters, temperature transmitters, high speed CPUs, and large data memory. The memory stores the physical properties of various fluids used in the temperature compensation formula under different pressures and temperatures, including density, viscosity, gas constant, compression coefficient, constant volumetric heat, etc. , Temperature, real-time, dynamic and most complete compensation calculation, the greatest degree of elimination of the factors causing the flow measurement error. For the steam flow measurement, the steam is automatically judged to be in a saturated, unsaturated, and hot state, and the compensation calculation is automatically performed. The measurement accuracy is about 1%. The measuring rod material is made of stainless steel and Hastelloy. The process temperature can reach 677°C.
Annubar flowmeter is particularly suitable for the measurement of gas and steam. The integrated Annubar flowmeter relative orifice flowmeter has the following main advantages: a single integrated assembly, saving components; no need for pressure tube; improve the reliability of the flowmeter Sex and measurement accuracy; reduce installation costs and time; reduce maintenance strength and costs; reduce potential leaks, reduce environmental pollution; reduce permanent pressure drop, save energy; better adapt to changes in device load.
1.2 Annubar Flowmeter Selection Considerations The mechanical dimensions of the Annubar flowmeter are tailored to the size of the pipe to be installed, and the flow measurement range is also calculated and calibrated based on the user-supplied flow data. Therefore, the provided flow data and pipe data must be correct, otherwise it will cause a large measurement error.
Although the T-type Annubar flowmeter has the nature of anti-blocking characteristics, but the following two situations need to pay attention to: 1 whether there are sticky impurities in the fluid impurities, such as non-electric decoking, dust water gas, tar in the gas and Dust, etc., adheres to the sensor, greatly affecting the measurement accuracy. 2 There are many impurities in the fluid, and the device is operated intermittently, with frequent stopping and long time. During the time when the flow stops, the impurities may dry out and foul on the surface of the sensor, which will clog the pressure port for years.
1.3 Application of Annubar flow meter The measurement of raw material gas CO and reboiler heating steam in the No. 1 acetic acid production plant of a certain factory is an orifice flow meter. The feed gas CO process is long, there are six orifice flowmeters, and the permanent pressure loss is large. With the constant increase of the device load, the compressor has to provide higher pressure to overcome the resistance loss, the orifice plate parameters (such as: differential pressure The data such as the range, volume, and density of the medium are set in advance. Unable to adapt to the dramatic increase in load and large fluctuations in load, resulting in very inaccurate raw material gas measurements. In the 2# acetic acid plant, the integrated Annubar mass flowmeter (which can perform real-time dynamic compensation of temperature and pressure) can be used. There is almost no permanent pressure drop and the measurement is accurate, which meets the requirements for continuous improvement of the load.
When the orifice flowmeter measures the steam flow, it is necessary to install a pressure-inducing pipe, a balance tank, an incubator, etc. The disadvantage is that there are many static seal points and it is prone to leakage. At the same time, in order to prevent freezing, steam heating or electric heat tracing is also required. With the constant increase of the device load, the orifice flowmeter has to change with the measurement range, even if the orifice plate reaming and so on, the measurement is not accurate, and the maintenance workload is also large. Therefore, in the 2# acetic acid plant, all the flow measurement of the vapors adopts the integrated Annubar mass flowmeter. According to the use situation, the measurement accuracy, the range of the range are large enough to meet the needs of expansion, no leakage, no maintenance, and the advantages are obvious.
2 electromagnetic flowmeter 2.1 The characteristics of electromagnetic flowmeter 1 electromagnetic flowmeter is based on Faraday's electromagnetic induction law work. Therefore, only the flow of conductive liquid can be measured, and the flow of gas, steam, and liquid containing a large amount of gas cannot be measured.
2 The electromagnetic flowmeter has no movable part and no flow blocking part, so there is basically no pressure loss, and liquid-solid two-phase flow such as slurry containing solid particles and sewage can be measured.
3 electromagnetic flowmeter only the pipe lining and the electrode contact with the measured liquid, so as long as a reasonable choice of electrodes and lining material, that can achieve corrosion resistance, wear resistance requirements, such as pulp, hydrochloric acid, hydrogen iodide and so on.
4 easy installation, as long as the full pipe, straight pipe ≥ 5D, straight pipe ≥ 2D, horizontal, vertical, inclined installation can be.
5 The measurement accuracy is high and can reach 0.5%. It can be used for the measurement of barrels, tankers, etc.
6 than the large range, usually 1:20, on-site can be based on needs, can expand or reduce the range, without parking.
2.2 The selection of electromagnetic flowmeters, the selection and installation of electromagnetic flow installations are very important links, and they are highly specialized. The following is a detailed introduction:
Applicable medium: whether the electromagnetic flowmeter can be applied is first judged according to the medium conductivity, the measured medium conductivity should be greater than 20μs/cm. The flow rate of the lower conductivity medium can be measured with a ceramic lining and platinum electrode electromagnetic flowmeter, but the ceramic lining is fragile and the use effect is not ideal.
Caliber selection: The diameter of the flowmeter is not necessarily the same as the diameter of the flowmeter. It depends on the flow rate. The process industry transports liquids with low viscosity such as water. The flow rate of the pipeline is generally an economic flow rate of 1.5-3 m/s. The electromagnetic flow is used on such a pipeline. The sensor diameter and the diameter of the pipe can be the same; it is used for easy adhesion, deposition, and knotting. The flow rate of fluids such as scales should not be lower than 2m/s, preferably 3-4m/s, and play a role of self-cleaning to prevent adhesion deposition; it is used for fluids with strong abrasion, such as slurry, and commonly used flow rates should be Less than 2-3 m/s to reduce the wear on the lining and the electrode; when measuring low conductivity liquids near the threshold, select the lower flow rate (0.5-1 m/s) as possible, as the flow noise increases the flow noise will increase, And output shaking phenomenon.
Material selection for flow-through parts: The parts of the sensor that come into contact with the liquid are linings, electrodes, grounding rings and sealing gaskets.
Commonly used lining materials include fluoroplastics, urethane rubber, neoprene rubber, and ceramics. The wear resistance, corrosion resistance, and the upper limit of the use temperature of the materials affect the adaptability of the instrument to the liquid. Fluoroplastics have excellent chemical resistance, but poor wear resistance, can not be used to measure the slurry, the use of temperature is less than 180 °C; neoprene for non-corrosive or weakly corrosive liquids, such as industrial water, waste water and weak Acid and alkali, the lowest price; urethane rubber has excellent wear resistance, but poor acid and alkali corrosion is suitable for coal slurry, pulp, etc., medium temperature is lower than 40 °C -60 °C/70 °C; alumina Ceramics have excellent abrasion resistance and corrosion resistance to strong acids and bases. They are suitable for corrosive slurries, but they are brittle and brittle when installed and clamped. They can be used at higher temperatures (120°C-140°C/180°C °C).
The corrosion resistance of the electrode to the measured medium is the first factor to consider in selecting the material, and secondly it is considered whether there will be surface effects such as passivation and noise formed. Electromagnetic flowmeter electrode corrosion requirements are very high, do not allow corrosion or strictly speaking only allow very low corrosion rate, otherwise it will destroy the seal between the electrode and the lining, commonly used metal materials are molybdenum-containing acid-resistant steel, Hastelloy Titanium, tantalum, and platinum-rhodium alloys cover almost all chemical solutions. There are also low-noise electrodes for slurries, such as conductive rubber electrodes, conductive fluorine plastic electrodes, and porous ceramic electrodes, or metals that wrap these materials. electrode.
The grounding ring is installed at both ends of the flow sensor connecting the plastic pipe or the metal pipe in the insulating lining. Their corrosion resistance is lower than that of the electrode. They are allowed to have certain corrosion, and they can be replaced regularly. Usually, acid-resistant steel or Hastelloy is selected. No grounding ring is required for the metal process pipe to directly contact the fluid.
Piping and Installation: Installation of electromagnetic flow piping that does not meet the requirements will cause the output of the flowmeter to oscillate, zero stability, short service life, and even damage. Mainly follow the following principles:
1 The upstream side of the sensor should not be close to valves, elbows and other devices that affect the flow of fluid; the downstream side can not install the pump to prevent the formation of negative pressure; throttling instruments such as regulating valves should be installed downstream of the flowmeter, especially barrels, device slots Cars and other empty pipes.
2 When designing the piping, ensure that the measuring tube is full, and that the upper and lower sections must maintain 5D and 2D straight sections.
3 The installation direction should pay attention to: when measuring the flow of liquid-solid two-phase medium, the sensor is properly installed vertically, and one can prevent the two-phase distribution of the liquid-solid two-phase medium from generating uneven or phase separation at a low flow rate. Reduce the additional error caused by this. Two can make the lining wear around the sensor more uniform, in the vertical installation, the flow direction should be from bottom to top, so as to ensure that the sensor is always full of media. In the horizontal installation, the connection between the two electrodes of the sensor should be horizontal, so if the medium contains bubbles, or if precipitation occurs, the input of the converter will not open.
4 Some conditions need to inject chemical drugs into the pipeline, which will lead to non-uniform conductivity of the liquid to interfere with the output signal of the electromagnetic flowmeter. In this regard, it can be injected downstream of the flowmeter. If it is to be injected upstream, the injection point should be kept at a distance from the flowmeter so that the liquid can be mixed evenly.
5 Ground loops must be used on plastic pipes or lining pipes.
2.3 The application of electromagnetic flowmeter A factory # 1 methanol low-pressure carbonyl process flow measurement instrument medium flowmeters are used in the orifice plate flowmeter under the following three kinds of process media conditions are not ideal, so in the 2 # device In the use of electromagnetic flowmeters, good results have been achieved. 1 The process medium containing hydroiodic acid is extremely corrosive. The orifice plate, pressure flange, root valve, and pressure guiding tube are made of zirconium alloy or Hastelloy, 1-inch to 8-inch orifice flowmeters. The price is 10-50 yuan/set. Therefore, in the 2# device, all the electromagnetic flowmeters are used, the lining material is PTFE, the electrode material is helium, and the price is between 3-10 million yuan/set, which saves a lot of costs. 2 acetic acid aqueous medium corrosive, 316L stainless steel pressure tube, root valve, ferrule, five valve group, etc. There is uniform corrosion, leakage occurs in about six months, the need to replace these parts, maintenance workload and high cost. The electromagnetic flowmeter was selected in the #2 device and it has been running well so far. 3 medium is acetic acid aqueous solution, iodomethane immiscible two-phase flow, orifice flowmeter is often due to easy to accumulate iodomethane phase (heavy phase) in the pressure tube lead to measurement error, affect the process operation, need frequent The liquid is discharged on site, the maintenance workload is large and the effluent is toxic, which endangers the health of operators. The electromagnetic flowmeter was used in the #2 device, and the measurement was accurate, which overcomes the disadvantages of the orifice flowmeter when measuring 2-phase flow.
Due to lack of experience, electromagnetic flowmeters are also used in 2# devices where they are unsuccessful: 1 The acetic acid conductivity is higher than 5μs/cm. We choose the ceramic lining. The ceramic lining is fragile. It is used during construction because of Causes of pipeline vibration, without exception, have cracked, leaked and damaged. 2 Do not use the temperature higher than 160 °C, otherwise it is easy to damage the PTFE lining. 3 When the finished product is measured at the top of the tower, the acetic acid of the finished product has low conductivity, the electromagnetic measurement accuracy cannot meet the requirements, and the measurement is inaccurate. After that, the mass flow meter is used to solve the problem. 4 The flow rate of the electromagnetic flowmeter should not be too high: there is a flowmeter with a diameter of 1 inch and the front and rear pipes are 3 inches. After the operation, the liquid flow rate in the flow tube reaches 7m/s, causing strong noise and violent vibration of the pipe. Replaced by 2-inch pipe diameter, the problem was solved. Therefore, in order to save the investment flow meter diameter, the design selection must not be too small. The flow rate selection has been discussed in 2.2.
3 Ultrasonic Flowmeter 3.1 Features of Ultrasonic Flowmeters Ultrasonic flowmeters can be measured in differential and Doppler modes. Doppler ultrasonic flowmeters can only be used to measure fluids containing media or particles that reflect the ultrasonic signals in a suitable amount. It is more demanding on the medium to be measured. It cannot be clean water, and the impurity content must be relatively stable. Stable measurement. At present, the most widely used and most widely used is the time difference ultrasonic flowmeter, which is mainly used to measure the clean fluid flow.
Time difference ultrasonic flowmeters can be divided into three types: externally attached, segmented, and plug-in type.
External paste type: There are two kinds of portable and fixed, installation of transducer without pipe cut off, that is, stick with it. The portable ultrasonic flowmeter has great maneuverability and is mainly used for temporary measurement of fluid flow in different pipelines, using a built-in rechargeable battery to power; fixed ultrasonic flowmeter in a certain fixed position, for the fluid in a specific pipeline The flow is measured continuously for a long time, using 220V AC power, with 4-20mA signal output and other functions.
Pipeline: The transducer and the measuring pipe are integrated and the measurement accuracy is also higher than other ultrasonic flowmeters. However, it must be cut off and cut to open the pipe before installation. However, the sensor can not be stopped for maintenance. The measuring tube is made of carbon steel, 316L stainless steel, Hastelloy C, etc. The integrated measuring temperature is up to 140°C. It can be used in high temperature mediums with a maximum temperature of 180°C. Can measure solids content <5% (by volume) or gas content <2% (by volume) of uniform fluid, measurement accuracy up to 0.5%.
Plug-in: In the installation, special tools can be used to create holes in the pipeline with fluid and insert the transducer into the pipeline. The signal is transmitted and received without passing through the pipe wall and the pipe lining, so its measurement is not affected by pipes and pipes. Lining material effects. The plug-in type sensor can avoid the problem of the coupling agent, and can realize stable and reliable measurement under the situation that the inner wall of the pipeline is heavily fouled or the gas contains fluid.
3.2 Comparison of sensor type selection 1 Ultrasonic portable ultrasonic flowmeters are easy to use and are most suitable for evaluating the flow conditions of pipeline networks or for checking the operation of other flow meters on pipelines.
2 There is no direct corrosion problem in the external-mounted sensor, but the corrosion and crystallization of the inner surface of the pipe can also cause inaccurate measurements.
3 outside the paste sensor due to the coupling agent in the use of a period of time prone to hair dry phenomenon, affecting the detection effect, in the larger diameter of the pipeline should not be used.
4 Paste sensors for short-term measurement with butter, esters such as Vaseline can also be used for long-term measurement of silicone or silicone.
5 Outside-mounted sensors are not suitable for measuring gases.
3.3 Installation of Ultrasonic Flowmeters The unreasonable installation of ultrasonic flowmeter transducers is the main reason why they cannot work properly. The installation of the transducer requires consideration of both the location determination and the choice of the method. In addition to ensuring adequate upstream and downstream straight pipe sections (first 10D, rear 5D), it is necessary to pay attention to where the transducers try to avoid contaminated point sources such as inverters and welding machines. In the installation method, there are mainly V mode and Z mode. Under normal circumstances, when the pipe diameter is less than 300mm, it is installed in V mode. When the pipe diameter is greater than 300mm, it is installed in Z mode.
3.4 Application of Ultrasonic Flowmeter In the acetic acid device, the 316L material-type ultrasonic flowmeter used for the low-conductivity and strong-corrosion pure acetic acid media replaced the original orifice plate and the ceramic-lined electromagnetic flowmeter and achieved good results, overcoming the orifice flow rate. Easily corroded leaks, high maintenance costs, and ceramic-lined electromagnetic flowmeters are easily crushable and do not resist damage due to severe temperature changes. The flow measurement of the original circulating water main (DN700) was a turbine flowmeter. After it was put into operation one year later, due to wear of the turbine flowmeter bearing, the measurement error was large, and after being replaced with an external clamp fixed ultrasonic flowmeter, the operation was stable, and the overrun was overcome. Turbine flowmeter bearings are relatively easy to wear and have a short lifetime.
In chemical companies, the cooling water of a single heat exchanger is generally not metered. However, sometimes it is necessary to calibrate the capabilities of each device to provide design basis for expansion, reconstruction and new installations. At present, we are in the process of designing the third set of 600,000-ton/year acetic acid plant. We will use a portable ultrasonic flow meter to measure the circulating water flow of the heat exchanger under the condition of no stopping. A large amount of data will be obtained so that accurate analysis and calibration can be performed. The capacity of numerous heat exchangers provides a reliable basis for better design of the third set of devices, while also saving the cost of installing many flow meters, and avoiding unnecessary losses due to parking of the devices.
Concluding remarks During the technological transformation of the acetic acid plant, the Annubar flowmeter was used to replace flowmeters such as orifice plates, turbines, and elliptical gears on the raw gas, steam, and methanol pipelines; electromagnetic flowmeters were used instead of highly corrosive hydrogen iodide and acetic acid. And the orifice flowmeter on the medium pipeline with conductivity >20μs/cm; replace the orifice plate, turbine and ceramic lining electromagnetic flowmeter on the pure acetic acid pipeline with low conductivity and strong corrosiveness by the pipeline type ultrasonic flowmeter; The portable ultrasonic flowmeter measures the flow of each circulating water user and so on to achieve the intended purpose. These new types of flow measurement instruments have their own unique characteristics and have been applied more and more widely in many fields. Each type of instrument is not a universal one. Therefore, in engineering applications, the correct selection is based on the process requirements and the characteristics of the medium. The design and installation of pipes and pipes are important links to the advantages of these meters and must be highly valued by us.
Lately, use of continuous mining machines has become order of the day to comply with environmental regulations, protect surface features and also to achieve increased production rate. As the concern for safety in mines increased and highly stringent regulations were put in place, it required mining machinery engineers to be highly conversant with such regulations.