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Waste Heat Recovery Plan Of Coal Gangue Tunnel Kiln
Feb 28, 2018


Basic situation of coal gangue kiln

Annual output of 30 million pieces of standard brick tunnel kiln production line 2, gangue furnace cooling temperature exhaust in 200-200 ℃, this scheme USES the heat tube heat exchanger in recycling cooling section of the flue gas waste heat for the workshop heating.


Introduction to heat tube technology and application


Working principle and basic characteristics of heat tube and heat tube heat exchanger.

The heat tube originated in the 1960s in the United States. In 1967, a stainless steel - water heat tube was first put into orbit and operated successfully. Once the theory of heat tube was put forward, it was highly valued by scientists from all over the world and carried out a great deal of research work, which made the heat tube technology develop rapidly. Heat tube technology is mainly used in aerospace field, our country since the 70 s study of heat tube, heat tube air - since the 80 s have developed gas heat exchanger, heat tube waste heat boiler, high temperature heat tube steam generator, high temperature heat tube air furnace and other kinds of heat tube products. Due to the carbon steel and water two phase gravity heat tube has simple structure, low cost, easy fabrication, basically solved the compatibility between carbon steel and water, make this kind of heat tube in power, chemical industry, drying and building materials are widely used in the business.


The basic working principle of the gravity heat tube as shown in chart 1, the typical heat tube is composed of shell, external heating surface extension, end cover, pulling the tube into a 1.3 x (10 1 ~ 10-4) Pa after negative pressure filling the right amount of working fluid, and then seal them.


When the evaporating section of the heat tube is heated, the vaporization of the working substance in the heat tube is vaporized, and the steam condenses into a liquid in the condensing section under the differential pressure differential, and then the evaporating section is caused by the action of gravity. This cycle is so circular that heat is transferred from one end to the other. The heat transfer principle of heat tube determines that the heat tube has basic characteristics:

High axial thermal conductivity, the heat tube internal mainly depends on the work liquid, liquid phase change heat transfer, the thermal resistance is very small, therefore has high thermal conductivity. Compared with silver, copper, aluminum and other metals, the unit weight heat tube can transfer several orders of magnitude of energy.

Good isotherm. The steam in the heat tube is saturated, and the pressure of saturated vapor is determined by the saturation temperature. The pressure difference of saturated steam from the evaporative segment to the condensing section is very small, so the heat tube has excellent isotherm.


Because the heat tube has the above structure and characteristics, the heat tube heat exchanger composed of the heat tube has the following advantages:

The heat tube heat exchanger can separate the cold and hot fluid through the middle baffle of the heat exchanger, even the single heat tube during operation. Because of the leakage of wear, corrosion, over temperature and other reasons, it is only a single heat tube failure, without the mixing of cold and hot fluid. So the heat tube heat exchanger can be used for easy, explosive, corrosion and other fluids.

The cold and hot fluid of heat tube heat exchanger is completely separated, and it is easy to realize the complete countercurrent heat transfer of cold and hot fluid, and obtain a large logarithmic temperature difference. Cold and hot fluid are outside the tube flow at the same time, because the tube in the fluid disturbance outside the tube flow of the heat transfer coefficient is much higher than tube flow of heat transfer coefficient, and outside the tube flow on both sides of the heating surface a full extension can be obtained. Such heat exchangers can be made very compact and used for the recovery of low grade thermal energy.

For the fluid with high dust content, the heat tube heat exchanger can adjust the layout of the heat tube at the design time, so as to solve the wear problem of the heat exchanger.

With heat tube heat exchanger used in corrosive flue gas waste heat recovery, can adjust the evaporation and condensation period of cold and hot sides to adjust the heat transfer area of the thermal resistance, so as to achieve the aim of adjustment of heat tube wall temperature, the heat tube to avoid the maximum corrosion area.


Application range of gravity heat tube heat exchanger.

Due to the excellent properties of gravity heat tube heat exchanger, the application scope of the heat tube heat exchanger is very wide, and several application fields are described below.

Application in power engineering. The main application is the heat tube heat exchanger used as the boiler's low-temperature air preheater to solve the corrosion, ash and wear of the low temperature preheater. The heat tube air preheater has the following advantages over the tubular air preheater.

1. The problem of air leakage can be solved thoroughly

2. Corrosion can be reduced. The reason is that the first wall temperature can be adjusted to avoid the temperature area of severe corrosion (the relationship between wall temperature and corrosion velocity is shown below). Second because of the heat tube with excellent isothermal property, so each heat tube wall temperature are basically a fixed value, and each of tubular air preheater tube wall temperature is a range, so that the boiler operation condition changes, all of tubular air preheater tube is likely to be severe corrosion in the area, and the heat tube air preheater is only part of the tube may be in severe corrosion area

3. It has good anti-fouling performance. Because corrosion and ash are two closely related problems, the solution of corrosion prevents the condensation on the tube wall, thus preventing the occurrence of serious ash accumulation. According to the experience, heat tube air preheater can be higher than the tubular air preheater tube wall temperature 30 ℃, it can greatly reduce dust and corrosion.              


Parameters and design basis of furnace kiln


Kiln parameter: Fan flow of cooling section.72000M3/h, Full pressure 1321MP, power 55KW.

Heating area: 1500M2.

Heating load press: 180 w/h.

Heating direct heat load: 1500X180=270 kw/h

Tube heat loss and thermal load margin of 15%.

Heat transfer of equipment : 270*1.15=310.5kw/h


Heat exchanger solution:

Inlet exhaust   gas temp

400

Outlet exhaust gas temp

150

Heat load

160

Hot water flow

6t/h

Cooling water   inlet temp

60

Hot water outlet   temp

80

Number

1

Material

Spiral finned tube heat tube.

Size

φ1.5×0.8×1.3height

Project features: Compared with conventional economizer and tube type air preset, heat tube has the characteristics of long life, large temperature drop, small volume and small maintenance.

unit in demand=310.5/160=2


Steam scheme thermal parameters and structural parameters.

Inlet exhaust gas temp

400℃

Outlet exhaust gas temp

170℃

Gas output

0.2 ton

steam pressure

0.3Mp

number

1

material

Spiral finned tube heat tube.

Size

φ2.3×0.9×2.7(height)


Benefit analysis of three heat exchangers

coal conservation: about 102KG/H

Annual coal consumption: 714 ton

Benefits for the whole year: 714X1000=714000

If the life expectancy of heat exchanger is 8 years, 5712000RMB will be saved. From the above data, it can be seen that the economic benefits are significant.


Thermal flow diagram:


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