1、 Overview

ASME nozzle is a high-precision flow measurement device that measures low pressure at the throat β The long necked nozzle device is commonly used for mainstream flow measurement in power plants, such as precise measurement of condensate flow in power plants, measurement of feedwater flow or steam flow in power plants, and high-precision flow testing sites such as fan performance tests and compressor performance tests.

In the analysis of thermal economic benefits of modern large-scale thermal power plants, in order to accurately determine the performance of steam turbine units, the measurement of the main condensate flow rate is very important. According to ASME standards, high-precision differential pressure components are used for flow measurement, and ASME standard nozzles are specified for engineering applications. This device is recommended by the American Society of Mechanical Engineers (ASME) and its superior performance has been widely recognized internationally. In many places where high-precision flow measurement is required, the ASME nozzle has become a solution.

2、 Measurement principle

The ASME nozzle adopts a throttling flow sensor. It adopts a special pressure measurement (throat pressure measurement) method based on the long neck nozzle, which not only has the advantages of traditional long neck nozzles, but also has the unique advantages of stable discharge coefficient and high repeatability. It is a high-precision flow sensor. Flow calculation formula:

In the formula: - represents the mass flow rate (kg/s) and the volumetric flow rate (m3/s) respectively;

——Discharge coefficient;

——Expansibility coefficient;

——Orifice diameter of throttling element, m;

——Diameter ratio,

——Pipe inner diameter, m;

——The density of the measured fluid, kg/m;

——Differential pressure, Pa;

3、 Characteristics

1. The structure is simple, easy to install, and widely used, mainly used in high-precision flow measurement occasions.

2. The pressure loss of the nozzle is small, and the straight pipe section length is required to be short.

3. Stable performance and high reliability.

4. It can withstand high temperature, high pressure, and impact.

5. The corrosion resistance is better than that of orifice plates and has a long service life.

6. The arc-shaped structure design can measure various liquids, gases, vapors, and other media.

7. High accuracy, good repeatability, and stable discharge coefficient.

8. It can be made of various materials and used in various performance experiments.

4、 Function and significance

1. Reduce the difficulty of unit performance testing, reduce the number of high-precision instruments used, and make it easier to obtain high-precision and good repeatability test results, which is conducive to achieving long-term, trend, and * performance monitoring of the unit.

2. Implement precise monitoring of the cold end of the steam turbine. Calculate the heat absorbed by the boiler through the feed water flow rate, and subtract the shaft power of the turbine from this heat to obtain the thermal load of the condenser. This method is not affected by system conditions. The improvement of measurement accuracy of condenser thermal load provides good conditions for effective analysis of condenser performance, and at the same time, accurate monitoring of circulating water flow can be achieved through condenser thermal load.

The performance status of the flow passage part of a steam turbine is generally reflected by the relationship between flow rate and pressure flowing through a given flow area. By verifying the flow and pressure relationship under a given flow area through high-precision feedwater flow, effective monitoring of the flow passage of the unit is achieved.

4. Due to the fact that the power output of the low-pressure cylinder accounts for about 50% of the total power output of the entire machine, it is crucial to timely grasp the performance of the low-pressure cylinder. However, determining the efficiency of the low-pressure cylinder has always been very difficult and must be completed through difficult performance assessment tests, which is difficult and costly. With the improvement of the accuracy of water flow measurement and the importance of leakage control in power plants, effective monitoring of low-pressure cylinder performance can also be achieved in general daily performance tests.

5. Due to the limitations of coal quantity measurement methods, the statistical error of the coal quantity entering the power plant is generally large, with low reliability, which is not conducive to energy-saving management. If the boiler's heat absorption is calculated based on the feedwater flow rate and accumulated, the cumulative value of daily or monthly heat absorption can be converted into standard coal quantity, and the accuracy of this quantity will be much higher than that of direct measurement of coal quantity. If used to verify the amount of coal entering the site or furnace, it will play a positive role in the management of coal yards in power generation enterprises.

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