Boiler Drying Out is necessary before the new boiler is put into production. 130t/h CFB boiler adopts high-temperature flue gas drying method, providing experience for CFB boiler drying out of other power plant.

130t/h CFB boiler features rated steam pressure 9.81MPa, steam temperature 540°C, feed water temperature 215°C, and flue gas temperature 140°C. The boiler adopts natural circulation, single-drum, open-air layout, centralized large-diameter downcomer, and full-membrane wall suspended closed structure. Water-cooled air distributor and air chamber; suspended and full-membrane water-cooled cyclone separator. Superheater is convection and radiation type, with two-stage spraying desuperheater; economizer is two-stage arrangement; air preheater is horizontal channel box.

Water-cooled cyclone separator adopts membrane wall, and is welded pins on inner wall, and casted 60mm thick high-temperature wear-resistant lining. The thickness of furnace wall reduces from 300～400mm to 50～60mm, thus the start-up has no limit. Cold start-up is 3-4 hours and warm start-up is 1～2 hours, which saves the cost of starting fuel. The service life of furnace wall in water-cooled cyclone separator is over 5 years, which reduces operation and maintenance cost.

 1. Optimization of Boiler Drying Out Process

The high temperature flue gas is to dry the circulating fluidized bed boiler. The flue gas generator generates hot flue gas, which is led to the area through the flue pipe.

1.1 Conditions Before Boiler Drying Out

(1) The flue gas system installation is complete, and the damper at ID fan outlet is operatable;

(2) Except the hot flue gas inlet, the remaining door openings shall be tightly blocked;

(3) All the refractory and wear-resistant materials masonry is complete and natural curing is more than 7 days;

(4) The expansion indicator is all complete, and the positioning pins of all spring hangers are removed before drying;

(5) The fire protection system is qualified, and the lighting is available;

(6) The industrial water and deaerator system is qualified;

(7) The steam-water, blowdown and drainage system is qualified;

(8) DCS flue gas temperature measurement system for furnace, separator, separator outlet flue duct, and ignition air duct are available;

(9) Exhaust electric valve is flexible, drum water level gauge, boiler water level and pressure monitoring system is qualified;

(10) The oil ignition system is qualified.

1.2 Boiler Drying Out Process

1.2.1 Drying Machine Start

(1) Start the drying machine at air chamber, run at little oil and low smoke temperature, gradually increase the oil amount.

(2) Start the drying machine at the furnace, run at little oil and low smoke temperature, gradually increase the oil amount.

(3) Start the drying machine at return valve, run at little oil and low smoke temperature, gradually increase the oil amount.

(4) Start the drying machine at upper outlet of furnace, run at little oil and low smoke temperature, gradually increase the oil amount.

(5) Start the drying machine at separator outlet, run at little oil and low smoke temperature, gradually increase the oil amount.

1.2.2 Temperature control

During the drying process, observe the temperature at the furnace, air chamber, separator, return port, etc., and check the deviation. Generally, the temperature shall not exceed  200°C at bag filter inlet, and 100°C at desulfurization tower inlet.

1.2.3 Drying Operation Caution

(1) Before drying, the boiler water level shall reach 100mm above the normal water level of steam drum;

(2) During the drying period, the drum pressure may gradually rise according to the drying temperature. Close the exhaust valve and open the drain valve to form water circulation. Pay attention to the drum water level during the filling process.

(3) During the drying period, monitor the flue gas temperature in the tail shaft and air preheater;

(4) During the drying period, check the expansion of boiler and flue duct, and record all the expansion data.

(5) The temperature difference between upper and lower walls of drum shall not exceed 40℃ during makeup feedwater.

(6) During the drying period, pay attention to data collection and analysis, and make adjustment in time.

2. Summary of Boiler Drying Out

The whole drying process shall adopt slow heating, uniform drying and strict temperature control to achieve ideal drying effect.

The residual moisture of refractory and wear-resistant materials is less than 2.5%, which meets the drying quality standard.