The elbow flow meter has its own unique advantages

　　The elbow flowmeter is installed at the bend of the pipeline to replace the existing elbow. It does not add new resistance, so it will not reduce the quality of steam during use. If the elbow flowmeter is used to replace the orifice throttling device, the initial pressure p1 of the steam turbine will be increased and the total outlet pressure p2 of the heating supply will be reduced under the condition that the outlet pressure of the boiler remains unchanged, thereby improving the power generation efficiency of the steam turbine, reducing the energy loss caused by the throttling element, and achieving the purpose of energy saving.

1. Characteristics of elbow flowmeter

The characteristics of the elbow flowmeter have been described in detail in the elbow sensor manual, which can be summarized as follows:

The structure is simple, there is nothing inside the sensor, and there is no additional resistance loss;

Strong, durable and wear-resistant, it can maintain sufficiently high measurement accuracy for a long period of time. Combined with the application of intelligent secondary instruments, the elbow flowmeter can be used as a measurement and assessment instrument.

High reproducibility, this feature is particularly suitable for measuring process flow and control flow;

Welding installation method ensures the long-term and leak-free operation of the elbow sensor.

It has low requirements for straight pipe sections, is very convenient to use in narrow devices, and has strong adaptability;

With different elbow materials and appropriate geometric dimensions, the elbow flowmeter can adapt to the flow measurement of most process media and process conditions in the alkali system; (the vast majority of process media mentioned here do not include the following special process media such as lime emulsion, alkali solution, etc. These two media are easy to deposit and scale, which will block the pressure pipe and are not suitable for flow measurement by elbow flowmeter (it is better to use electromagnetic flowmeter). As for refined brine, ammonia brine, etc., elbow flowmeter can be used for flow measurement. Therefore, it can be said that the scope of application of elbow flowmeter is very broad);

2. Devices and media suitable for flow measurement using elbow flowmeter

1. Kiln gas and furnace gas system

a. Air flow at lime kiln inlet

In order to save energy and reduce consumption, the motors of lime kiln blowers are all changed to variable frequency speed regulation to replace the traditional energy-consuming control method of adjusting the air volume. The energy-saving effect is of course very obvious. However, the orifice flowmeter installed to measure the actual air volume of the lime kiln will also cause additional resistance loss and increase the power consumption of the motor. If the orifice flowmeter is replaced by an elbow flowmeter for flow measurement, the pipeline resistance loss can be further reduced, thereby achieving better energy saving and consumption reduction. (Since the blower vibrates relatively strongly, the vortex flowmeter is not suitable here at all.)

The control object of frequency conversion speed regulation can be the air pressure or air flow rate of the lime kiln. Some units may not have the air flow rate detection of the lime kiln, which is very unfavorable for the optimization operation of the lime kiln. The two parameters of air pressure and air flow can not only conveniently control the output of the kiln, but also more conveniently understand the actual resistance in the kiln and judge the height of the material layer in the kiln. Taking advantage of the characteristic of the elbow flowmeter that it does not increase the resistance, it is a practical idea to add the detection of the air flow rate of the kiln.

b. Measurement of the air volume of steam turbine compressor

The air volume of the steam turbine compressor (whether it is kiln gas or furnace gas) is a very important process parameter. Due to the large pipeline, it is difficult to install the orifice flowmeter. At the same time, excessive resistance loss will greatly increase the load of the compressor. Therefore, the monitoring of this parameter is abandoned in the design, which is very detrimental to the safe operation of the steam turbine compressor.

The elbow flowmeter is particularly suitable for use in situations with large pipe diameter, large flow and low pressure (the pressure of carbon dioxide gas at the outlet of the steam turbine compressor is not low). It will not increase the load of the steam turbine compressor. If in actual construction, our company's on-site transformation technology is used to transform the existing standard elbow into a elbow sensor, the construction difficulty is very small and this transformation task can be completed very conveniently.

C. Carbonization tower lower gas, middle gas, cleaning gas flow detection

When several or dozens of carbonization towers are operated in parallel, it is very important to reasonably allocate limited gas resources. Therefore, the flow detection of the lower gas, middle gas and cleaning gas of the carbonization tower is indispensable. Replacing numerous orifice flow meters with elbow flow meters will inevitably greatly reduce the load of the steam turbine compressor, which is definitely beneficial to energy saving and consumption reduction.

D. Light ash calcining furnace outlet gas flow detection

The load of the light ash calcining furnace can be achieved by controlling the amount of heavy alkali entering the furnace (heavy alkali is measured by an electronic belt scale or a solid impulse scale). However, for heavy alkali with relatively high water content, it is very difficult to accurately measure solid materials. Therefore, steam consumption is generally used to indirectly estimate the actual load level of the calcining furnace. If the outlet gas flow of each light ash calcining furnace can be measured at the same time, it will be very beneficial for accurately estimating the actual load level of the calcining furnace. Since the cooling and purification system of the furnace gas is not one-to-one corresponding to the light ash calcining furnace, there is almost no type of flow meter that can effectively detect the flow before the furnace gas is cooled and purified. Therefore, the light ash calcining furnace does not have a single furnace gas flow meter, which is undoubtedly a defect for optimizing the operation of the calcining furnace. The elbow flow meter can better solve this problem. The high-temperature furnace gas carrying a large amount of soda ash dust will not cause too much trouble for the accurate measurement of the elbow flow meter. It can easily measure the actual furnace gas volume of a single light ash calcining furnace without increasing the load of the compressor. This is a good solution.

2. Steam system

In the alkali making system, steam is generally divided into medium-pressure steam and low-pressure steam, both of which are almost all superheated steam.

The steam at the boiler outlet, steam turbine, steam turbine compressor, steam turbine vacuum machine inlet, light ash calciner inlet, and heavy ash calciner inlet with slightly lower temperature and pressure all belong to the category of medium-pressure steam, which is characterized by relatively high temperature and pressure. A large amount of low-pressure steam is mainly used in mother liquid distillation tower and dilute liquid distillation tower. Almost all of these steam flows are orifice flowmeters (or quarter-circle nozzle flowmeters), and their main disadvantages are large resistance loss, easy leakage, and very difficult maintenance.

The welded installation method and lower straight pipe section requirements make the elbow flowmeter particularly suitable for measuring steam flow.

a. Medium pressure steam

The characteristics of medium-pressure steam are relatively high temperature and pressure. The elbows used in medium-pressure steam pipelines have a relatively large bend-to-diameter ratio, generally between 4 and 6. As long as a special elbow sensor with a corresponding bend-to-diameter ratio of 4 to 6 is used, the dual requirements of measurement and safety can be met. The welding installation method of the elbow sensor fundamentally solves the major problem of easy leakage of the steam flow measurement device. The advantage of no resistance loss can also achieve better economic benefits. It is wear-resistant and has a long period of operation without maintenance and repair, which reduces the operation and maintenance costs to the lowest point.

b. Low pressure steam

The technical difficulty of meeting the requirements of low-pressure steam flow measurement is even lower. A standard elbow sensor with a bend-to-diameter ratio of 1.5 can meet the dual requirements of measurement and safety. It should be mentioned here that the mother liquor distillation tower and the dilute liquid distillation tower use a large amount of steam, and the steam pipes are relatively thick, while the internal space of the device is relatively narrow. It is difficult to meet the more stringent straight pipe section requirements of other flow meters. Therefore, the measurement of steam flow here becomes a problem. The elbow flowmeter only needs a very short straight pipe section, and the front and rear straight pipe sections are on both sides of the elbow sensor, which is easy to meet the requirements.

3. Water system

For underground or semi-underground water pipelines, the flow meter is more required to be durable, because it is sometimes very difficult to repair these devices, and people hope that the flow sensor can achieve long-term reliable operation after one installation. The elbow flow sensor has the characteristics of being sturdy, durable, wear-resistant, and able to maintain sufficiently high measurement accuracy for a long period of time, which can play the greatest role here.

In the water system, special mention is made of the flow measurement of acidic water in chemical water treatment. In the process of chemical water treatment, since the water is acidic, the pipes are lined with rubber. For this special measured medium, as long as the acid-resistant stainless steel elbow sensor is selected, the flow measurement problem can be easily solved. As for boiler water supply, although the pressure and temperature are relatively high, there is no problem in using an elbow flowmeter to measure the flow.

4. Other media

The conventional method for measuring the ammonia flow rate of the absorption tower is to use a rotary vane flowmeter to measure the liquid ammonia. The rotary vane flowmeter is a mechanical flow measurement device, which has very high requirements for the cleanliness of the measured medium. A small amount of impurities may cause the instrument to be stuck and affect the normal operation of the instrument. Moreover, the high-speed rotating bearings are also prone to wear. If an elbow flowmeter is used to measure the gasified ammonia, the effect will be more ideal. Of course, since the density of ammonia is relatively small, the flow rate will not be too high, so a differential pressure transmitter with a relatively small differential pressure value is used. As long as this requirement can be met, measuring ammonia will not be a problem.

Gases similar to ammonia, such as coal gas, liquefied gas, acetylene gas, etc., can all be measured using bent tube flowmeters.

5. Boiler air supply volume

For large boilers, the automation level is relatively high. In order to improve the thermal efficiency of the boiler, the boiler air volume is a must-measure parameter. However, the boiler air supply duct is generally square and vibrates relatively large. Conventional flow measurement devices are difficult to meet the requirements. If an elbow flowmeter is used to measure the boiler air supply, we can modify the less standard square air supply duct bend to make a non-standard elbow sensor, so that this measurement problem can be effectively solved. Of course, the measurement accuracy of this modified elbow sensor is limited, but it still retains the advantage of good repeatability. As long as necessary corrections are made, it can meet the measurement requirements for the boiler air supply.