Thermal calculation of DKVr-6.5-13 boiler unit

Introduction

The purpose of the course design is to reconstruct a boiler unit of DKVr type with a steam capacity of D = 6.0t/h with excess pressure of superheated steam P = 13kgf/cm2 for solid fuel combustion .

Boiler reconstruction consists in obtaining steam of higher parameters. To do this, a superheater is installed behind the furnace, while removing part of the pipes of the first boiler bundle along the gas flow.

Design calculation of water economizer from cast iron ribbed pipes of VTI type is also carried out to more completely remove heat from flue gases and to reduce emissions to the atmosphere.

The calculation of DKV6,513 low-power boiler with steam capacity of 6.0 hour will be presented below.

DKV boilers are used with a longitudinal arrangement of the drum, and the lower drum is shortened, which allows placing a grate and a combustion chamber covered with screens in the front of the boiler. Water enters the screens from the headers, and the steam-water mixture is withdrawn to the front of the drum. Lowering pipes serve simultaneously as supports of front part of upper drum, and rear part of drum rests on pedestal through pipes of boiler bundle and lower drum.

Vertical partitions are provided between the tubes of the boiler bundle, which provide for more complete washing of the tubes with gases as a result of horizontal turns. When superheater is installed, it is placed behind right partition instead of part of pipes of boiling bundle.

All heating surfaces except screen tubes are convective heated from flue gases. So, if the temperature of the flue gases at the outlet of the furnace is about 1000 0C, then at the outlet of the last heating stage it will be 100150 0C.

1.2 Fuel combustion method selection

The combustion method is selected depending on the type of fuel, the physicochemical characteristics of the fuel and ash, the capacity of the boiler and its design features. When burning solid fuel, mainly layer and chamber furnaces are used.

1.3 Selection of exhaust gas temperature

The temperature of the exhaust gases is one of the main factors determining the efficiency of the boiler. Thus, a decrease in the temperature of the exhaust gases by 12-16 C increases the efficiency of the boiler by 1%.

In general, heat losses with exhaust gases are the largest among the losses in the heat balance of the boiler and are usually 5-12%.

The selection of the optimal temperature of the exhaust gases is based on a feasibility study. This is due to the fact that a decrease in the temperature of the exhaust gases, on the one hand, leads to an increase in the efficiency of the boiler, and on the other, to the need to increase the area of ​ ​ convective surfaces and the cost of traction and blowing. In addition, the minimum temperature of the exhaust gases is limited by the low temperature corrosion conditions of the heating end surfaces. The temperature of the exhaust gases is also selected taking into account the cost of fuel, its humidity, values ​ ​ of the feedwater temperature and steam pressure.

Recommended temperatures of exhaust gases during solid fuel combustion: ¼ u.g = 120-150 ° С. We take to = 145 ° С.

1.4 Selection of heating tail surfaces

The choice of the tail heating surfaces involves solving questions about the feasibility of installing a water economizer and air heater on the boiler under consideration, as well as determining their layout.

For low pressure boilers, air with a temperature of 25-34 ° C is used as a blast, which eliminates the need to install an air heater. In these boilers, an economizer made of ribbed cast iron pipes is usually installed. In boilers with a capacity of D < 25 t/h, having developed surfaces, are limited to the installation of only a water economizer.

The water economizer is an integral part of the modern steam generator. The economizer, thanks to the use of small diameter pipes, is an inexpensive and compact heating surface in which the heat of exhaust gases is effectively used. In modern steam generators, the water economizer receives up to 18% of the total amount of heat transferred through the heating surfaces of the steam generator. Economizers are made of pipes with a diameter of 28-38 mm, which bend into coils, usually located in a downhole gas duct during transverse washing with their combustion products. The location of the coils is most often staggered, maybe corridor, the collectors are round in shape, usually located outside the gas duct.

To facilitate the installation of the economizer, the convenience of repair work and the facilitation of cleaning from fly ash, the heating surfaces are divided into separate units.

Conclusion

In this course design, the boiler unit DKVr6,513 was heat calculated. According to the task and type of fuel used in combustion

in the steam generator, we calculated the enthalpy, the volume of air and combustion products from the gas ducts of the boiler. The heat balance of the boiler was calculated, as a result of which the design characteristics of the furnace chamber were determined, the temperature of the gases at the outlet of the furnace was determined.

Next, a single-stage superheater was designed and the necessary heat-receiving surface was obtained for it. In the following calculations, we made a check calculation of two boiler bundles, and determined the amount of heat received by the heating surface.

The final stage was the constructive calculation of the low-temperature heating surface: a single-stage water economizer.

The lack of heat balance of the boiler did not exceed 0.5% of the amount of heat available, and as a result, the entire calculation can be considered complete and correct.

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