During normal operation, the basic principles for adjustment of  bed temperature: 

1. During normal operation, the bed temperature shall be controlled at 920℃ ± 40 ℃, it shall not be higher than 980 ℃, it is forbidden to exceed 1000 ℃; It shall not be lower than 840 ℃, it is forbidden to be below 800 ℃. 

2. During normal combustion, the primary air shall account for 55-60% of total air amount, on one hand, it can guarantee the combustion share of dense-phase zone, on the one hand, it can make the dense-phase area zone burn in reducing atmosphere, thus reducing NOx emissions. The reasonable adjustment of the air distribution ratio of the primary air and the secondary air can reach the best burning effect of the boiler unit. 

3. Maintain reasonable ash circulation quantity and ensure that the returns from the materials-returning feeder can completely return back the hearth. Keep the temperature of returns inside the materials returning feeder at about 950 ℃ and maintain the stability of bed temperature. 

4. The main means of adjusting the bed temperature are adjusting the coal charging quantity to the boiler and adjusting the primary air volume to the air distribution plate. If the bed temperature rises, the coal feed quantity shall be reduced or the coal feed shall be reduced within short time. When the coal feed is reduced, it shall not be completely reduced. The coal feeder shall not be stopped. If the bed temperature  decreases, the coal feeding shall be increased or the coal feeding shall be increased within short time. When the coal is fed, it is required to supply air firstly and then to feed coal. When the coal is reduced, it is required to reduce coal first then to reduce air quantity. 

5. If the bed temperature rises, it is possible to appropriately increase the primary air quantity  and to appropriately reduce the secondary air quantity, reduce the coal feed quantity and increase the materials returning quantity. But attention shall be paid to the temperature at the outlet of the superheated steam in order to beware of over temperature. If the bed temperature drops, it shall be timely adjusted. 

6. If the bed temperature is reduced, it is possible to decrease the primary air volume, increase the coal feed quantity and decrease the materials returning quantity. But attention shall be paid to the temperature at the outlet of the superheated steam, the attemperation water flow shall be adjusted. If the bed temperature rises, it shall be timely adjusted. At this time, part of the ash accumulated in the materials- returning feeder can be discharged. 

7. If the bed temperature changes greatly, at the same time when the primary air and materials-returning volume are appropriately adjusted, the coal feed can be greatly decreased or increased, but attention shall be paid to the changing trend of bed temperature, and the coal feeding shall be adjusted timely according to the changing trend of bed temperature. 

8. If the overheating steam temperature changes, it is possible to appropriately adjust the volume of the secondary air. 

Factors affecting the change of the bed temperature during operation: 

1. The change of load, the change of fuel amount (including coal feeding interrupted, coal shedding and coal blocking etc.), the change of coal quality and particle size, the change of returns, the change of air volume, the change of bed pressure, the causes shall be timely analyzed, and the measures shall be taken to maintain normal and stable bed temperature. 

2. When the boiler load change causes the bed temperature to change, it is possible to adjust the primary air volume, the secondary air volume, the coal feed volume and materials returning volume to adapt the change of boiler load. The load of boiler is adjusted through adjusting the proportioning ratio of air and coal and the proportioning ratio of primary air and the secondary air. 

3. If the boiler load is greatly reduced, at the same time, the coal feeding amount shall be reduced, the primary and secondary air flow and the air volume for material-returning  shall be reduced. When the primary air flow is reduced, attention shall be paid to that the air volume to the air chamber is not less than the minimum fluidization air volume in order to keep the hearth in good state of fluidization. If the boiler load increases greatly, the primary and secondary air flow and the air flow for material-returning shall be increased and the coal feed and circulating ash amount shall be increased too. 

4. If the bed temperature decreased due to the change of coal feed, on condition that the good fluidization of bed layer is guaranteed, the primary air volume can be appropriately reduced and the coal feed quantity can be increased. If the bed temperature drops quickly, the primary air volume and the air pressure for returns shall be appropriately reduced in order to reduce the ash returning quantity and at the same time part of the accumulated ash in the returns feeder shall be discharged. 

5. The coal supply from the coal feeder is interrupted, is arching and is blocked, thus causing temperature to decrease at outlet of the hearth and the oxygen amount indicated in the oxygen gauge to increase,  the coal interrupting shall be handled in time and the coal feeding rotating speed shall be increased. 

6. The coal quality suddenly gets better, at this moment, the temperature at outlet of hearth, the steam temperature and bed temperature have a tendency to rise, the content indicated in the  oxygen gauge decreases, which shows the coal amount is large. In order to stabilize working condition, the coal feed amount shall be reduced. 

7. The coal quality suddenly gets poor, at this moment, the temperature at outlet of hearth, the steam temperature and bed temperature have a tendency to decrease, the content indicated in the oxygen gauge increases, at this moment, the bed temperature shall be controlled. 

8. The coal particle size suddenly becomes smaller, resulting in a decrease of combustion share in dense-phase zone and  reduction of bed temperature drop. At this time, it is required to increase the primary air amount and the secondary air amount, but not to increase the coal feed amount, for fear that the combustion share in dilute phase zone increases and after burning of circulating  ash to cause  overheating and coking of return feeder. Coal particles suddenly become larger, resulting in a increase of combustion share in dense phase zone and a increase of bed temperature and no changing of indication of oxygen gauge, it is required to increase the primary air amount and to decrease the secondary air amount. 

9. The slag is not discharged timely, the materials layer is thickened, resulting in a decrease of amount of primary air  and a increase of differential pressure of material layer and bed temperature, so the slag shall be discharged. 

10. The ash is blocked in return feeder, so the circulation of ash from return feeder is stopped, and the bed temperature increases, at this moment,  part of circulating ash shall be discharged timely, in order to make the return feeder unblocked. 

11. The indication of oxygen content does not change, and the bed temperature gradually decreases, and the whole combustion temperature increases, part of circulating ash shall be discharged in order to make the bed temperature rise.