Study of Design Theory and Application Software Development of Correct Calculation for Air Heaters Performance Test

Based on performance test of tri-sector rotary air heaters, the paper briefly proposed a correct calculating method of gas temperature, air temperature, air leakage rate and resistance. A Correct calculation software of air heaters performance test was developed. It can normalize and unify computation, solve some problems such as the organic combination of manual intervention and computer calculation and the cyclic iteration of some parameters. The study will help to improve speed and accuracy of computation, improve the efficiency of the economy and cost savings, enhance the competitiveness of power generators, and has an important utility value.


Introduction
As last heating surface, the air heaters plays an important role in air heating and waste heat recovery of gas leaving steam-water endothermic section .The air heaters couples air and flue system, coal pulverizing system, combustion system and so on. Air heaters thermal performance test is usually required to test performance of air heaters for the thermal power unit. The air heaters thermal performance usually includes gas side efficiency, air leakage rate, correct coefficient, gas-air resistance and gas temperature. At present, the widely-adopted code are Chapte 8.6 of GB/T 10184-2015 Performance test code for utility boiler [1]and Air heaters performance test codes: ASMEPTC 4.3-2017 [2]. But GB/T 10184-2015 Performance test code for utility boiler only provides basic definitions and simplified formulas for air heaters , and do not related to air leakage rate and resistance Correct calculation. It is short of important content such as thermal performance, X ratio, air leakage rate correction, resistance test, so Air heaters performance test codes: ASMEPTC 4.3-2017 is used in most acceptance test in China. Before 2017, the version is Air heaters performance test codes: ASME PTC 4. . Before this code was finalized, no tri-sector rotary air heaters was invented, so it should apply only to bisector rotary air heaters. North China Electric Power Research Institute wrote Air heaters performance test codes in order to regulate and help performance test of air heaters and apply to new equipment.
The purpose of air heaters performance test is identify thermal performance of air heaters. The difference between actual test and design condition is unavoidable in the process performance test. In order to compare with design performance of air heaters, test results need to be revised to design condition. Based on studying the outcomes in related fields at home and aboard, Air heaters performance test codes gave a correct and interoperable correcting computational method of air heaters performance test. To facilitate application of Air heaters performance test codes, the study design calculation software. It can normalize and unify computation, solve some problems such as the organic combination of manual intervention and computer calculation and the cyclic iteration of some parameters, and help to improve speed and accuracy of computation, supply reliable and precise data for optimization and varying operation of air heaters. The paper regards one power plant as an example, combine calculated calculation software with real data to evaluate the reasonableness in difference between actual and design condition. It is beneficial to study air heaters performance, devise optimization strategy of system operation for the operators, and improve the stability of boiler combustion and the efficiency of the economy and cost savings, enhance the competitiveness of power generators, and has an important utility value.

Gas temperature correction
Compared to design conditions, the influence of change parameters such as air leakage, inlet air temperature, inlet gas flow, inlet gas temperature, heat capacity ratio, air mass on outlet gas temperature of air heaters should be calculated in process of actual test. The calculation formula is as follows fg.lv.nl.cr fg.lv.nl cr.a.en cr.fg.en cr.fg.qm a.en.ds t Is inlet air design temperature of air heaters, ℃. The change of inlet gas temperature causes the change in exhaust gas temperature , the calculation formula of correct value is as follows.
fg.en.ds t Is inlet gas design temperature of air heaters, ℃. The change of inlet gas mass causes the changes in some parameters such as air velocity, the average temperature, heat transfer coefficient. The calculation formula of correct value is as follows:

Air leakage correction
In tri-sector rotary air heaters, the gas bin next to primary air bin and secondary air bin. There is a considerable difference in air leakage between air bin and gas bin. The calculation formula of air leakage ratio is as follows: is The design difference between inlet pressure of primary air bin and outlet pressure of gas bin, Pa.

The function of program
The program can control the order of thermodynamic calculation and perform calculation of performance test correction of air heaters by combining air model, coal model, gas model and air heaters model. The overall structure of software is shown in Figure 1.  Figure 1. The overall structure of software.

Coal category
Coal is the main fuel of coal-fired power plant. There are many classification methods of coal in China. The content of components is different for different coal. The sum for each content of component should be equal to 100. The main function of the coal category as follow: judge whether the sum equal to 100.

Gas category
Main functions of gas category: Set and calculate the related parameters of gas. Take one power plant as an example, input the related parameters to main program. The calculation results are as follows.  The difference between primary air pressure and gas pressure pa 11645 5 The difference between secondary air pressure and gas pressure pa 2695.5 6 The difference between primary air pressure and secondary air pressure pa 8949.5 7 Air leakage temperature ℃ 65.01 8 The design difference between primary air pressure and gas pressure pa 15145 9 The design difference between secondary air pressure and gas pressure pa 5145 10 Air outlet temperature ℃ 337.00 11 Air design enthalpy of air heaters inlet KJ/kg.℃ 5.351 12 Air leakage factor from primary air to secondary air / 0.74 13 Air leakage factor from primary air to gas / 0.65 14 Air leakage factor from secondary air to gas / 0.35

Air heaters category
Main functions of air heaters category mainly includes four parts: gas temperature correction, air temperature correction, air leakage correction and resistance correction. The gas temperature correction include correction taken into the inlet air temperature change, correction taken into the inlet gas temperature change, correction taken into the inlet gas mass change and correction taken into XR deviate from the designed. The resistance correction include gas resistance correction and air resistance correction. The overall structure of software is shown in Figure 2: Main functions of air heaters category: Set and calculate the related parameters correction computation of air heaters performance test. To return to the example of one power plant, input the related parameters of coal, air, gas and thermal power unit to main program. The calculation results are as follows: