Parameter design and selection basis of drum dryer Henan Hongxing

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Parameter design and selection basis of drum dryer

rattler-drying machinery The key to the design is to determine the overall size, that is, to determine the effective length of the drum and the effective heat transfer diameter. At present, there is no theoretical method to determine the cylinder radius and the cylinder length. Design is completely based on experience (laboratory experience, design experience and operating experience). In fact, both physical meaning and mathematical method have the conditions to determine the key dimensions of the drum, only need someone to confirm the effectiveness and accuracy of a certain method.

 rattler-drying machinery

1. Determination of the length of drum dryer

Structure and drying principle of drum dryer Once the ash is cooled to a temperature that does not need further cooling or cannot be further cooled, the cooling process should be terminated. In fact, the ash is pseudo cold in the drum. In order to extract as much heat as possible and send back to the power generation cycle, it is necessary to determine the effective length of the drum theoretically.

The effective length of the drum dryer can be determined according to the theoretical criterion that the effective cooling temperature difference is zero. That is, the ash temperature is close to or equal to the cooling water temperature. But in fact, due to the relationship between the small specific heat of ash and slag and the pseudo cooling of ash and slag, the change rate of ash temperature (whether the average temperature calculated by the model or the measured value in the laboratory) is much higher than the temperature of cooling water, and the cooling curve close to constant is shown after the ash moves for a certain distance. The effective length of drum dryer should be the length when the ash cooling curve becomes constant with time as the theoretical length. Even if the ash temperature is still decreasing, it will be of no economic significance to use a large amount of metal to recover a small proportion of heat.

2. Determination of diameter of drum dryer

Drum diameter determines the key size of drum dryer. There is no theoretical method to determine the diameter of drum dryer at present. We explore a simple method which can be used in industrial practice.

The heat transfer rate, i.e. the heat transfer per unit time and unit heat transfer area, is still a quantity related to the location. Therefore, we can only discuss the average heat transfer rate of the whole drum, not the specific traditional area heat transfer rate. No matter the results of laboratory measurement or industrial operation, the average heat transfer rate can only be the operating value under specific conditions, and the heat transfer rate will change with the change of operating parameters.

The heat transfer rate at different filling rates was measured on a 200 mm diameter water-cooled drum, and the corresponding mathematical description was established. Two contents can be seen from the measurement results of heat transfer rate under different filling rate. One is that there is a filling rate in the drum with a specific structure, which can obtain the heat transfer rate. One is that the heat transfer rate is restricted by the rotational speed of the drum, and the heat transfer rate varies greatly with the same filling rate.

After the accurate heat transfer rate is obtained, the heat transfer area requirement of a specific drum dryer can be obtained according to the heat transfer coefficient (empirical value or measured value under similar working conditions), and the drum diameter can be obtained by combining the drum structure and engineering experience. According to the measured results of 150 MW unit, the heat transfer rate of drum dryer at actual operating speed is 0.7 kJ / s, which is much higher than the measured value in laboratory. The reason may be that with the increase of the device size, the restriction of the roller structure on the particle movement is significantly reduced, and the ash has more opportunities to release heat.

The ash handling capacity of drum dryer corresponding to heat transfer rate is not only an important assessment index, but also an important factor to determine the drum diameter. However, because the drum is a heat transfer device, the ash movement is closely related to the ash heat transfer coupling, so the ash handling capacity is physically subject to the heat transfer rate. As long as the roller structure can ensure the appropriate axial forward speed, the three important performance indexes of heat transfer rate, slag discharge temperature and ash handling capacity are consistent.

 Drum drying workshop

3. Main basis for selection and use of drum dryer

The particle size distribution of several kinds of coal with ash content more than 20% is compared with the measured value of particle size distribution of bottom slag. It can be seen that the size distribution of bottom slag formed by coal with high ash content is closer to the particle size distribution of raw coal. The performance of soft coal and hard coal shows that the particle size of soft coal bottom slag is larger than that of hard coal.

Each kind of coal into the furnace has its own operation characteristics, which needs users to find out by themselves. With the characteristics of ash formation and bottom slag, the operation can be guided. According to the distribution ratio of ash and lime for different coal types without considering limestone, the conditions of different fuel calorific value, ash content and boiler slag discharge share are considered.

After the user decides to use the drum dryer, it is important to determine the appropriate product. It can ensure the limited recovery of the physical sensible heat of ash and slag; second, it can ensure a simple boiler to the design; third, it can provide design convenience for the downstream ash conveying system; fourth, it can provide sufficient convenience for operation and maintenance. Red Star drum dryer to meet the above four conditions, welcome to Hongxing dryer manufacturer Investigate the purchase of the machine.

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