Safe and energy-saving bagasse drying system for sugar refinery

Abstract

The invention relates to the field of energy-saving drying systems, in particular to a safe and energy-saving bagasse drying system for a sugar refinery, which comprises boiler waste flue gas (passing through an air preheater), a high-pressure blower, a heat pipe type heat exchange system, a bagasse drying device, a cyclone separator and a flue gas purification system, the boiler is provided with an air preheater for recovering heat, and waste flue gas of the boiler is connected with the heat pipe type heat exchanger after passing through the air preheater; the flue gas purification system is connected with the other end of the heat pipe type heat exchanger, and the other end of the heat pipe type heat exchanger is emptied; the bagasse drying device is connected with the heat pipe type heat exchanger, and bagasse to be dried enters the drying device to complete heat exchange. According to the bagasse drying system for the sugar refinery, waste heat discharged by the boiler can be used for heating the normal-temperature atmosphere in the heat pipe type heat exchanger device, so that heat exchange is completed; and the bagasse drying device uses heated hot air for drying, so that the bagasse is dried to a reasonable water content, the energy consumption is greatly reduced, and resources are reasonably utilized.

Description

Technical Field

[0001] The system of the invention relates to the field of safe production and energy-saving systems, and more specifically, to a safe and energy-saving sugar mill bagasse drying system. Background Art

[0002] The uses of sugar mill bagasse mainly include papermaking, production of paper products, preparation of functional cellulose derivatives, preparation of microcrystalline cellulose, as fuel, edible fungus culture medium, and a large amount of use in the field of modification, making outstanding contributions to environmental protection. The uses of bagasse are so wide, and the amount of bagasse produced by sugar mills during the crushing season is huge, and its moisture content is about 50%, which is difficult to preserve and easy to grow mold. Therefore, the bagasse must be dried to a certain moisture content to make it easy to preserve and transport, etc. The usual value is 12%-15% moisture content.

[0003] At present, the sugar mill bagasse drying methods can be divided into two types based on the drying heat medium: 1. Use the waste heat flue gas from the boiler to directly pass into the dryer and mix with bagasse for drying. The disadvantages of this method are: such high-temperature gas (generally the flue gas temperature is not less than 170℃ after multiple waste heat utilization) is mixed with some coal ash, and the coal ash carries sparks, etc., which can easily cause the bagasse to be ignited and explode during the drying process, causing safety hazards to production and personnel. Secondly, the coal ash particles carried in the flue gas cause secondary pollution to the bagasse, greatly reducing the utilization value of the bagasse and increasing the cost of bagasse reprocessing.

[0004] 2. Drying with superheated steam. The disadvantage of this method is that it consumes a lot of energy, is not conducive to energy conservation and emission reduction, is not environmentally friendly, affects the steam used in sugar factory production, and greatly increases the steam production load.

[0005] Therefore, it is necessary to propose a sugar mill bagasse drying system that solves the above problems. Summary of the invention

[0006] The present invention is to overcome at least one defect (deficiency) of the above-mentioned prior art and provide a safe and energy-saving sugar mill bagasse drying system.

[0007] The technical solution of the present invention is as follows: A safe and energy-saving sugar mill bagasse drying system, comprising an air preheater (1), a flue gas high-pressure fan (2), a heat pipe heat exchange device (3), a flue gas purification system (4), an air high-pressure fan (5), and a bagasse drying device (6), characterized in that: After passing through the air preheater (1), the boiler waste flue gas is connected to the lower heat exchange chamber of the heat pipe heat exchanger (3) under the pressure of the flue gas high-pressure fan (2); the boiler flue gas (waste gas) passes through the air preheater (1), the air preheater (1) is connected to the heat pipe heat exchanger (3), and a flue gas high-pressure fan (2) is provided between the air preheater (1) and the heat pipe heat exchanger (3) to assist (the air supply fan should be connected to the connecting pipe between the air preheater (1) and the heat pipe heat exchanger (3) at a certain angle, and the direction is the same as the flue gas flow direction); the flue gas purification system (4) is connected to one end of the heat pipe heat exchanger (3), and the other end is emptied; one end of the air high-pressure fan (5) is connected to one end of the heat pipe heat exchanger (3); one end of the bagasse drying device (6) is connected to one end of the heat pipe heat exchanger (3); The other end of the cyclone separator (7) is connected to the heat pipe heat exchanger (3) through the air preheater (1) (assisted by the flue gas high-pressure fan (2) in the middle), and then emptied after being purified by the flue gas purification system (4) to meet the standards, thereby forming a passage; the normal temperature and pressure atmosphere enters the heat pipe heat exchanger (3) through the air high-pressure fan (5), and then enters the bagasse drying device (6), and then emptied after passing through the cyclone separator (7), thereby forming another passage; the high-temperature boiler flue gas and the normal temperature and pressure atmosphere exchange heat in the heat pipe heat exchanger (3), and clean and high-temperature air is obtained to dry the bagasse, so that the waste heat of the flue gas is further utilized, energy consumption is reduced, resources are reasonably utilized, and the bagasse drying process is safe and reliable.

[0008] Furthermore, the heat pipe heat exchanger (3) is a highly efficient heat transfer element having extremely high thermal conductivity and excellent isothermal properties, and its heat recovery efficiency is over 90%. The heat pipe is composed of metal pipes sealed at both ends, and is filled with a working fluid inside. The working fluid absorbs heat and evaporates at the high-temperature end, and then the vapor flows up to the low-temperature end to release heat and condense. The liquid working fluid flows back to the high-temperature end under the action of its own weight, and heat exchange is repeated in this way.

[0009] The heat pipe heat exchanger (3) is composed of a baffle (31), a heat pipe (32), a partition (33), a lower heat exchange chamber (34), a conical ash collection chamber (35), an ash leakage hole partition plate (36), and an upper heat exchange chamber (37); the heat pipe heat exchanger (3) is designed to be divided into two parts, with a partition (33) in the middle. The partition (33) is arranged with multiple rows of vertical heat pipes (32). The upper heat exchange chamber (37) is supplied with normal temperature atmosphere by a high-pressure air blower (5). The lower heat exchange chamber (34) is connected to the boiler waste heat flue gas from the air preheater (1). The heat pipe (32) heats the working medium in the pipe by discharging heat from the boiler waste heat gas and then exchanges the heat to the normal temperature clean gas in the upper heat exchanger (37). The boiler waste heat flue gas and the gas of dried bagasse in the heat exchanger (3) are separated into upper and lower parts and do not interfere with each other. One end of the lower heat exchange chamber (34) of the heat pipe heat exchanger (3) is connected to the air preheater (1) (with the assistance of a flue gas high-pressure fan (2) in the middle), and the other end is connected to the flue gas purification system (4) to form a channel; one end of the upper heat exchange chamber (37) of the heat pipe heat exchanger (3) is connected to the air high-pressure fan (5), and the other end is connected to the bagasse drying device (6) (its air inlet and bagasse feed inlet are mixed), and then connected to the cyclone separator (7) to form a channel; when the flue gas from the air preheater (1) passes through the high-temperature gas to the lower heat exchange chamber (34) of the heat pipe heat exchanger (3), the heat pipe (32) uses the introduced heat to quickly heat the medium in the pipe and boil it to form steam, thereby quickly and efficiently transferring heat to heat the normal-temperature air in the upper heat exchange chamber (37) of the heat exchanger, thereby completing the heat exchange.

[0010] Furthermore, an ash removal device (9) is provided below the heat pipe heat exchanger (3). By providing the ash removal device (9), during the passage of flue gas through the heat pipe heat exchanger (3), ash and coal particles carried by the flue gas will be deposited, and the ash and coal particles will be removed in a timely manner, thereby ensuring that the heat pipe heat exchanger (3) can be unobstructed, and the heat exchange is more thorough, efficient and safe.

[0011] Furthermore, a thermal insulation layer (8) is provided on the outside of the heat pipe heat exchanger (3), and the provision of the thermal insulation layer (8) reduces heat loss.

[0012] Furthermore, the thermal insulation layer (8) is made of cement perlite products or glass fiber products. In practical applications, the thermal insulation layer (8) may also be made of other materials, all of which are within the protection scope of the present invention.

[0013] Furthermore, the gas is atmospheric air at normal temperature and pressure, and the clean air at normal temperature of the heat pipe heat exchanger (3) is heated by introducing high-temperature flue gas, thereby achieving a heat exchange effect.

[0014] Furthermore, there is at least one bagasse drying device (6). In practical applications, multiple bagasse drying devices (6) can be connected as needed, all of which are within the protection scope of the present invention.

[0015] Furthermore, the heat pipe heat exchanger (3) is at most one. In practical applications, a plurality of heat pipe heat exchangers (3) can be provided as required to form one or more groups of heat pipe heat exchangers (3), all of which are within the protection scope of the present invention.

[0016] Furthermore, each of the flue gas high-pressure fans (2) and air high-pressure fans (5) at each position must be equipped with at least one spare blower of the same model.

[0017] Compared with the prior art, the beneficial effects of this system technical solution are: The bagasse drying device system disclosed in the present invention uses a heat cycle exchange device (3) between the high-temperature flue gas from the air preheater (1) and the bagasse drying device (6). The upper and lower heat exchange chambers of the heat exchange device (3) operate independently, so that the waste heat flue gas discharged from the boiler heats the clean normal temperature atmosphere in the heat exchange device (3) without polluting the normal temperature air. The bagasse drying device (6) uses the heated clean gas to dry the bagasse from the sugar factory. In this way, since the waste flue gas discharged from the boiler and the hot air for drying the bagasse are independent of each other, the dangerous event of explosion caused by the mixed drying of the boiler flue gas and the bagasse during the drying process is avoided, and the secondary pollution of the bagasse raw material is eliminated, so that the sugar factory can obtain qualified dried bagasse and reduce energy consumption. The most valuable thing is that the safety hazard is eliminated in the drying process. As the saying goes, life is priceless, and resources are used safely and reasonably. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The invention discloses a structural schematic diagram of a safe and energy-saving sugar factory bagasse drying system.

[0019] In the figure: 1-air preheater, 2-flue gas high pressure fan, 3-heat pipe heat exchanger, 4-flue gas purification system, 5-high pressure blower, 6-bagasse drying device, 7-cyclone separator, 8-insulation layer, 9-ash removal device, and the wet bagasse material inlet and the clean hot air from the heat pipe heat exchanger (3) enter the inlet of the bagasse drying device (6) for mixing.

[0020] Figure 2 It is a schematic structural diagram of the heat cycle exchange device in the present invention.

[0021] In the figure: 1-air preheater, 2-flue gas high pressure fan, 3-heat pipe heat exchanger, 4-flue gas purification system, 5-air high pressure fan, 6-bagasse drying device, 9-ash removal device.

[0022] Figure 3It is a schematic diagram of the structure of the heat pipe heat exchanger in the present invention.

[0023] In the figure: 3-heat pipe heat exchanger, 31-baffle, 32-heat pipe, 33-partition plate between upper and lower heat exchange chambers of heat exchanger, 34-lower heat exchange chamber of heat exchanger, 9-ash removal device, 35-conical ash collection chamber, 36-partition plate with ash leakage holes (also serves as a fixed heat pipe), 8-insulation layer, 37-upper heat exchange chamber of heat exchanger. DETAILED DESCRIPTION

[0024] The drawings are only used for illustrative purposes and are not to be construed as limitations of the present invention. To better illustrate the present embodiment, some parts of the drawings may be omitted, enlarged, or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the drawings.

[0025] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation" and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. It can be said that the internal connection of two components is connected. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. The technical solution of the present invention is further explained below in conjunction with the accompanying drawings and embodiments.

[0026] like Figure 1 As shown, a safe and energy-saving sugar factory bagasse drying system comprises an air preheater (1), a flue gas high-pressure fan (2), a heat pipe heat exchanger (3), a flue gas purification system (4), an air high-pressure fan (5), a bagasse drying device (6), a cyclone separator (7), and also includes a material (wet bagasse) inlet (i.e., a clean hot air inlet from the heat pipe heat exchanger (3)); after a portion of heat is recovered through the air preheater (1) of the high-temperature boiler flue, it is connected to the lower heat exchange chamber (34) of the heat pipe heat exchanger (3) with the assistance of the flue gas high-pressure fan (2), and the other end is connected to the flue gas purification system (4) for purification and then discharged, thus forming A passage; clean normal temperature air enters the upper heat exchange chamber (37) of the heat pipe heat exchanger (3) through the air high pressure fan (5), and after heat exchange in the chamber, it is connected to the bagasse drying equipment (6) and dries the wet bagasse before entering the cyclone separator (7) for purification and then emptied, which forms another passage; these two passages, with the heat pipe heat exchanger (3) as a hub, exchange heat in the heat pipe heat exchanger (3) with the high temperature waste flue gas with ash particles and sparks coming out of the air preheater (1) to obtain high temperature clean air, thereby drying the bagasse, making the process safe and reliable, environmentally friendly and energy-saving, and making rational use of resources to achieve the purpose of carbon emission reduction.

[0027] like Figure 2 As shown, the heat pipe heat exchanger device (3) comprises an upper heat exchange chamber (37) and a lower heat exchange chamber (34) of the heat exchanger and a dust removal device 9; the heat pipe (32) in the upper heat exchange chamber (37) of the heat pipe heat exchanger (3) is generally provided with a heat dissipation fin and a baffle (31), the medium heated by the upper heat exchange chamber (37) of the heat exchanger is clean air at room temperature, and one end of the lower heat exchange chamber (34) of the heat pipe heat exchanger (3) is connected to The air preheater (1) is connected to the air preheater (1) (the waste flue gas from the air preheater (1) passes through the lower heat exchange chamber (34) of the heat pipe heat exchanger (3) with the assistance of the flue gas high-pressure fan (2), and the other end is connected to the flue gas purification system (4) to form a channel; one end of the air high-pressure fan (5) is connected to one end of the upper heat exchange chamber (37) of the heat pipe heat exchanger (3), and the other end is connected to the bagasse drying device (6) to form a passage. When the high-temperature flue gas from the air preheater (1) passes through the lower heat exchange chamber (34) of the heat pipe heat exchanger (3), the vertical heat pipe (32) in the heat pipe heat exchanger (3) uses the heat introduced to quickly conduct heat to heat the clean air at normal temperature in the upper heat exchange chamber (37) of the heat pipe heat exchanger (3). In the system of the present invention, an ash removal device (9) may be provided under the heat pipe heat exchanger (3). By providing the ash removal device (9), the heat exchange chamber (34) in the lower half of the heat pipe heat exchanger (3) is regularly cleaned during operation to prevent ash accumulation on the heat pipe from affecting the heat exchange effect.

[0028] like Figure 3As shown, the heat pipe heat exchanger (3) is composed of two upper and lower heat exchange chambers, a conical ash collecting chamber (35) and an ash removal device (9) are provided at the bottom, and the main heat exchange device is composed of an upper heat exchange chamber (37) and a lower heat exchange chamber (34), with a vertical heat pipe (32) in the middle. When designing, the volume space of the upper heat exchange chamber (37) is larger than the volume space of the lower heat exchange chamber (34), which is determined according to the performance of the working medium in the heat pipe (32) (the lower half of the working medium in the heat pipe (32) is liquid, and after the lower half is vaporized, it rises to the upper heat exchange chamber (37) and then heat-exchanges and cools to become liquid, which flows back to the lower part under the action of its own weight, and reciprocates (these liquid-gas phase conversions are all carried out in the heat pipe (32)), and the liquid occupies much less space than the gas), and the middle partition (33) completely isolates the upper heat exchange chamber (37) and the lower heat exchange chamber (34) into two independent spaces without interfering with each other. The upper heat exchange chamber (37) is provided with a baffle (31), and the heat pipe (32) is provided with fins as required to facilitate heat exchange. Flue gas from one end of the air preheater (1) enters the lower heat exchange chamber (34) of the tube heat exchanger (3), and the working medium in the heat pipe (32) is boiled and vaporized within a very fast time, rises to the upper heat exchange chamber (37), and then exchanges heat with the clean normal temperature air passing through the upper heat exchange chamber (37). After the working medium releases heat, it cools into liquid and returns to the heat pipe (32) in the lower heat exchange chamber (34) under the action of its own weight, and then absorbs heat and vaporizes, and the cycle repeats. The clean air at normal temperature is designed to enter from the lowest temperature of the upper heat exchange chamber (37) (delivered by the high-pressure air blower (5)), and after multiple deflections, it undergoes a heat absorption process from low temperature to high temperature, and then comes out from the highest temperature and enters the bagasse drying device (6) in order to maximize the heat exchange efficiency (the fins on the heat pipe (32) and the baffles (31) in the heat exchange chamber are both intended to achieve this effect). A partition with holes is provided between the lower heat exchange chamber (34) of the heat pipe heat exchanger (3) and the ash collection room (35), which can not only fix the upright heat pipe (32) but also allow the ash in the flue gas to be deposited and discharged into the ash collection room (36) through the holes, so that the ash is discharged from the ash discharge device (9) at a regular time to ensure the heat exchange effect and the normal and safe operation of the system.

[0029] In the system of the present invention, the heat pipe heat exchanger (3) is provided with insulation on the outside. Figure 1The insulation layer (8) shown in the figure reduces heat loss during the operation of the system by setting the insulation layer (8), wherein the insulation layer (8) is made of cement perlite products or glass fiber products. In practical applications, the insulation layer (8) can also be made of other materials, all of which are within the protection scope of the system of the present invention. In the system of the present invention, the heat pipe heat exchanger (3) can be designed according to production needs, and the number of heat pipes (32) therein is set according to actual production needs. The heat pipe heat exchanger (3) is generally designed to have a large upper heat exchange chamber (37) and a small lower heat exchange chamber (34). This is designed based on the working fluid in the heat pipe (32) and the rationality of heat conductivity. In practical applications, one or more heat pipe heat exchangers (3) can be connected as needed, all of which are within the protection scope of the system of the present invention.

[0030] Example In this embodiment, when it is necessary to dry the bagasse from the pressing workshop of the sugar factory, the waste heat contained in the high-temperature gas from the boiler flue gas after passing through the air preheater (1) can be used to heat the normal-temperature atmosphere in the upper heat exchange chamber (37) through the heat pipe heat exchange device (3) to achieve heat energy exchange. The high-temperature flue gas of 200-250° C. from the air preheater (1) enters the lower heat exchange chamber (34) of the heat pipe heat exchanger (3) through a pipeline with the assistance of a high-pressure blower (2). The high-temperature flue gas releases sensible heat in the lower heat exchange chamber (34), and the heat exchange pipe (32) of the heat exchange chamber converts this part of the sensible heat into latent heat and transmits it to the upper heat exchange chamber (37), and releases heat to heat the normal-temperature atmosphere in the upper heat exchange chamber (37). In this process, the thermal efficiency of the heat pipe (32) is as high as 90%, which is a theoretical value. In practice, it may be slightly lower, but it is also within the scope of protection of the present invention.

[0031] We take the 55-ton boiler expanded in a sugar factory in Yunnan as an example. Its designed flue gas emission is 500,000 Nm3 / h. Excluding the air leakage in the intermediate pipeline and the air supply behavior factors, it is estimated that the flue gas volume passing through the air preheater is about 1 / 5-1 / 6 of the emission, that is, about 80,000-100,000 Nm3 / h. The thermal enthalpy of the 250℃ high-temperature flue gas is about 2700 KJ / KG (KJ / KG and KJ / Nm3 are equivalent), that is, the heat discharged from the air preheater with the flue gas per hour is about 216 million KJ-270 million KJ of heat. This part of heat is converted into heat by the tubular heat exchanger (3) and used to dry the bagasse raw material. The daily crushing capacity of the sugar factory is 3500 tons, and the daily output of bagasse is about 1400 tons. Even if only a part of the heat is used (the thermal efficiency of the tubular heat exchanger (3) is up to 90%), it can still meet the production demand. After the flue gas passes through the heat pipe heat exchanger (3), the exhaust flue gas temperature also drops to 120-170°C (this is a theoretical value estimated based on Newton's law of conservation of energy. There may be deviations in practice, but it has also been confirmed in previous boiler inspections). This prevents the sulfur dioxide in the flue gas from generating sulfuric acid (the dew point of sulfuric acid is 98°C) when it meets water, thereby corroding the equipment. This is just an example to illustrate that the thermal efficiency can meet the production demand. In reality, it can be reasonably designed and adjusted according to production requirements to achieve the purpose of energy saving and emission reduction and reasonable use of resources. The above examples are all included in the protection scope of the claims of the present invention.

[0032] In the figure, the description of the positional relationship is only for illustrative purposes and cannot be understood as a limitation on the present invention; obviously, the above-mentioned embodiments of the present invention are only examples made to clearly illustrate the present invention, especially the boiler expansion of a sugar factory in Yunnan, which is only used to illustrate the flue gas enthalpy, and is not a limitation on the implementation methods of the present invention. For ordinary technicians in the field, other different forms of changes or modifications can be made on the basis of the above description. It is not necessary and impossible to list all the implementation methods here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A safe and energy-saving sugar factory bagasse drying system, comprising an air preheater (1), a flue gas high-pressure fan (2), a heat pipe heat exchange device (3), a flue gas purification system (4), an air high-pressure fan (5), and a bagasse drying device (6), characterized in that: The boiler exhaust gas passes through the air preheater (1) and is then connected to the lower heat exchange chamber of the heat pipe heat exchanger (3) under the pressure of the flue gas high pressure fan (2); One end of the heat exchange chamber (34) in the lower part of the heat pipe heat exchange device (3) is connected to the boiler exhaust gas coming out of the air preheater (1), and the other end is connected to the flue gas purification system (4); The bagasse drying device (6) is connected to the upper heat exchange chamber (37) of the heat pipe heat exchanger (3). The bagasse completes heat exchange in the drying device (6). After drying, the bagasse is divided and packaged. The dried gas enters the cyclone separator (7) and is purified to meet the standards before being discharged.

2. A safe and energy-saving sugar factory bagasse drying system according to claim 1, characterized in that: The heat pipe heat exchanger (3) is composed of a baffle (31), a heat pipe (32), a partition (33), a lower heat exchange chamber (34), a conical ash collection chamber (35), an ash leakage hole partition plate (36), and an upper heat exchange chamber (37); the heat pipe heat exchanger (3) is designed to be divided into two parts, with a partition (33) in the middle. The partition (33) is arranged with multiple rows of vertical heat pipes (32). The upper heat exchange chamber (37) is supplied with normal temperature atmosphere by a high-pressure air blower (5). The lower heat exchange chamber (34) is connected to the boiler waste heat flue gas from the air preheater (1). The heat pipe (32) heats the working medium in the pipe by discharging heat from the boiler waste heat gas and then exchanges the heat to the normal temperature clean gas in the upper heat exchanger (37). The boiler waste heat flue gas and the gas of dried bagasse in the heat exchanger (3) are separated into upper and lower parts and do not interfere with each other. The heat exchange chamber (34) at the lower part of the heat pipe heat exchanger is divided into an air inlet end and an air outlet end, wherein the air inlet end is connected to the boiler waste heat flue gas from the air preheater (1), and the air outlet end is connected to the flue gas purification system (4); One end of the upper heat exchange chamber (37) of the heat pipe heat exchanger is connected to one end of the air-gas high-pressure blower (5), and the other end is connected to the air inlet end of the bagasse drying device (6).

3. A safe and energy-saving sugar factory bagasse drying system according to claim 2, characterized in that: A dust removal device (9) is provided at the lower part of the heat exchange box (3).

4. A safe and energy-saving sugar factory bagasse drying system according to claim 2, characterized in that: A heat-insulating layer (8) is provided on the outside of the heat exchange box (3).

5. A safe and energy-saving sugar factory bagasse drying system according to claim 4, characterized in that: The thermal insulation layer (8) is a cement perlite product or a glass fiber product.

6. A safe and energy-saving sugar factory bagasse drying system according to claim 2, characterized in that: The drying gas is normal atmospheric air.

7. A safe and energy-saving sugar factory bagasse drying system according to claim 1, characterized in that: The bagasse drying device (6) is composed of one or more vertical drum dryers.

8. A safe and energy-saving sugar factory bagasse drying system according to claim 1, characterized in that: The air supply fans are a flue gas high-pressure fan (2) and an air high-pressure fan (5), both of which have at least one spare air supply fan of the same model.

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