| Coal dominates Chinese energy consumption which has low efficiency,meanwhile large amounts of nitrogen oxides, sulfur dioxide, dust and other solid pollutants are generated in coal combustion. In winter, supply heating is required in Northern China, To reduce pollutant emission of the smaller capacity and widely used heating boiler is one of most important directions for energy saving and emission reduction.It is planted to replace the low efficiency and highly polluting chain heating boiler by high efficiency and low pollution pulverized coal heating boilers in S. Germany GTK Group and France Pillard Company provided four retrofitting plans. Scheme one is that the chain of boiler is dismantled, pulverized coal burners are installed, and all the equipment which are above the furnace arch will be moved upward to form burning space. Scheme two is that the chain of boiler dismantled, pulverized coal burners are installed and other devices are not moved. but it is required to prevent air leakage in the bottom of the furnace, so fireproof is installed. Scheme three is that pulverized coal burners are installed on both sides of the chain in the furnace; meanwhile the boiler is required thermal design and calculation.Scheme four is that the furnace arch and chain are completely dismantled, and Natural gas burner is installed in the bottom of the furnace. The third retrofitting plan is selected under considering of the characteristics of heating boiler long operating at low load and the heating boiler highly daily load change rate. The acceptable swirl burner on industrial heating pulverized coal boilers is designed for T Baocheng boiler plant which will complete the total renovation work. And the cold modeling experiment is required to verify the rationality of the design.The limited volume of the retrofitted boiler and the combustion characteristic of selected inferior coal were considered. The residence time for coal particles in boilers is required more than 2s in order to ensure sufficient combustion. That coal and air flow would not scour the opposite water-cooled wall, so the length of the torch can not exceed 5.8m. At the same time, it should also have a larger re-circulation zone to ensure the stable combustion of coal flow.Firstly, swirl burner that met the above requirements was designed by thermal design calculation, structure calculation and flared design for the burner outlet. Secondly the burner was produced according to the drawings. Thirdly, the swirl burner cold model test unit was designed and built up. The unit includes measurement system and control system. Then 8 optimal designs with better mixing and disturbance characters were selected from 27 designs with flow field observation. The 8 optimal designs flow fields are measured. The best design is that 13 °primary air flared angle, 13 °secondary air flared angle, 16m/s primary air velocity, 21m/s secondary air velocity. In this time, the residence time of pulverized coal gas flow in boiler is about 2.125 s, flame length is about 5.3m, central recycling zone length measured is about 2m(5 times diameter of the secondary duct), the radial distance is about 0.7m(1.5 times diameter of the secondary duct), and the maximum re-circulation velocity is about 6m/s. The results show that the designed swirl burner boiler fulfills the requirement of T Baocheng boiler plant. |
PDF Full Text Request