Abstract: A special chain-steam boiler applied to biomass briquette was devised through optimum design and performance test to overcome the shortcoming of traditional biomass boiler which had low degree of mechanization and high pollution.The design foundation included the component analysis of biomass briquette, the combustion characteristic of biomass briquette and the main technical parameters of the special chain-steam boiler.The boiler had single longitudinal layout drum and water-fire tube shell, and its combustion equipment was chain grate.Water-cooled wall was installed on both the left and right sides of the furnace, and convection banks fixed on the flanks, while screw smoke tube convection heating surface applied in the drum.During the boiler working, biomass briquettes with certain particle size were fed into chain grate by feed hopper, and then burning in the furnace.The high-temperature flue gas was generated by combustion flowed along the bottom of the drum, then entered the convection banks on the flanks through the export of boiler smokestack, and then entered the convection heating surface of screw smoke tube through the frontal smoke chamber.Passing through economizer and deduster, the exhausted gas was discharged into atmosphere through chimney pumped by induced-draft fan finally.Innovation of the boiler was the new structure of the furnace which has front, middle and rear arch on the upper part of the chain grate to form more efficient air dynamic field.The stability of combustion was improved on account of the arrangement of the arch crown and combustion chambers, and the combustion efficiency was improved also for the high fitting degree of chain grate and furnace in this design.In addition, the screw smoke tube in the drum, which may strengthen the effect of convection heat transfer, could also raise the thermal efficiency of this boiler.For the purpose of achieving to the national standard, new type water film dust collector was chosen to decrease the discharge quantity of atmospheric pollution in the exhaust smoke.Experiments were carried out in the pilot plant of Henan Agricultural University on March 2015.Three different types of biomass briquette were combusted to test the thermal performance and environmental index of the chain-steam boiler.These experiments continued 7 days, and the boiler operated normally 6 h each day.The test results showed that the combustion efficiency of this boiler reached 96.7%, and the thermal efficiency was 83.2%.The output of steam was 984 kg/h, while the temperature of steam reached 173 ℃, and the pressure of steam 0.7 MPa.Furthermore, the content of CO in the exhaust smoke was 360×10-6, and 116×10-6 for that of NO_x.For SO₂, the content was 44×10-6, while 26.4 mg/m3 for smoke dust.The test data indicated that combustion and thermal efficiency of the new boiler were higher than traditional boilers.Moreover, powerful smoke removing function could be achieved by this new boiler, and contents of smoke dust, nitrogen oxide and sulfur dioxide in the exhaust smoke are low enough to meet the national standard.