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          Design of four seasons air cooled mobile combined dehumidifier in shipyard

          Author:Lianzhong | Release time:2021-06-15

          Abstract: the four season air-cooled mobile combined dehumidifier used in shipyard mainly includes refrigeration system, treatment air heating system, runner dehumidification system and electrical control system. This paper discusses the design methods and key points of these systems in detail through the design calculation of specific examples.

          Key words: dehumidification, refrigeration, runner, heating, four seasons, mobile

           

          Design of Air-cooling Removable Combined Dehumidifier Used

          in Shipyard and Operated ALL Year Ro und

               Abstract:The air-cooling removable combined dehumidifier is widely used in shipyard and   operated all year round there. This kind of dehumidifier mainlyconsists of the refrigeration  system,heating system of process air, rotor dehumidifying system and electrica| control system. ln this paper`,the design methods and ther key points of these systems are discussed in detail throughthe design calculation of a demonstrat on example

              Keywords:dehumidify,refrigeration ,rotor;heating;operated all year roung;removable

          1 Preface

                  Shipyards have high requirements for rust prevention and anti-corrosion treatment of hull surface during shipbuilding or ship repair. Before painting, the hull must be polished and derusted. The metal surface after derusting treatment must be kept quite dry before painting. That is to say, the treated hull metal surface must be kept in a dry air environment. Generally, the relative humidity of the air should be below 40%, And maintain the appropriate working environment temperature, such a requirement can not be achieved by simple refrigeration dehumidification system or simple wheel dehumidification system, but must use the combination of refrigeration and wheel dehumidification and temperature regulation. In addition, shipyards need to build or repair ships all year round, and for large shipyards, there are many docks and painting workshops, and the built or repaired hulls are often large. Therefore, the dehumidifiers used must be able to operate all year round and be hoisted to different places or positions by cranes, Therefore, the dehumidifier used in the process of shipbuilding or ship repair in shipyard must be a four season air-cooled mobile combined dehumidifier.

          2. Processing flow, principle and design parameter requirements

                  The treatment flow of four seasons air cooled mobile combined dehumidifier is shown in Figure 2-1, which is mainly composed of refrigeration system (including surface cooler)   Dehumidification system of runner (including dehumidification runner, runner drive system and heating regeneration system)   The electric heating system and electric system of air treatment system are composed. The surface cooler and runner dehumidification respectively refrigerate and absorb the air buried at the place. The electric heater of the treated air is used to adjust the temperature of the treated air in winter, and it can also be used to adjust and open the refrigeration system in spring and autumn seasons to ensure the normal operation of the dehumidification function in the four seasons of the year.

                  Because of the high moisture content of outdoor air under the limiting working conditions in summer, it will increase the difficulty of regeneration of runner, which will require increasing the regeneration heating temperature. However, due to the limited high temperature resistance of the runner and high temperature, the runner will be burned. Therefore, the regeneration air will be cooled by the surface first, and then part of the humidity is removed, and then heated for regeneration of the runner.

                   Generally, the design parameters of the four seasons movable air-cooled combined dehumidifier used in shipyards are shown in table 2-1.

          3. Specific system design

                  In this paper, the air volume of dehumidification treatment is g=10000m γ h. Other design parameters are the same as table 2-1 for example. The design parameters of four seasons air cooled mobile combined dehumidifier are discussed in detail.

                 According to the design requirements in table 2-1, the outlet temperature TN ≤ 3O ℃ and relative humidity RHN ≤ 40% in summer are considered. In order to ensure that the design meets the requirements, the values of the air temperature and relative humidity are less than, but close to 30 ℃ and 40% respectively. Similarly, in winter, the air temperature and relative humidity of the treatment are more than 15 ℃ and less than 40%, but are very close to 15 ℃ and 40% respectively. In addition, the temperature of the treatment fan should be considered in the design, generally estimated to be about 1 ℃.

                   When the runner is dehumidified, the dehumidification treatment air flows through the runner 3 to suppress it   The area of the regenerative heating air flows in the reverse direction through the area of 1/4 of the runner. The surface wind speed of dehumidification treatment air passing through the runner is 2,5-4m/s or the mass flow rate is 3-48kg / M2S, and the air volume of regeneration air is generally 1 / 4-1 of the treated air  / 3. Jing   After the regeneration is heated to 120-140 ℃, it flows through the runner in reverse direction and then empties directly; Now, the high efficiency silicone runner is basically adopted, with the speed of 8-10r / h [1].   The runner manufacturer has the performance curve table of runner or runner selection calculation software for designers to select runner and design calculation system.

          3.1 refrigeration system

                 Take the most unfavorable (limit) environmental meteorological parameters in summer as the design parameters of air inlet in table 2-1, namely tw=40 ℃  , RHw=95%。   The specific dehumidification process of the summer treated air is shown in Figure 1-D as shown in Figure 3-1.

                According to the 1-D diagram and runner selection calculation software (or performance curve), during the above Figure 3-1 treatment, the dehumidification treatment system and the runner regeneration system treatment points

             

          The parameters are shown in table 3-1, in which the air volume of regeneration air is designed to be 1 / 3 of the air volume of treatment air passing through the runner, the regeneration temperature is designed to be 20 ℃, and the mass flow rate of treatment air passing through the runner is designed to be 3,3kg / m2. S (i.e. the surface wind speed is 2.75m/s). It can be seen from Figure 3-1 and table 3-1 that in summer, the treated air is cooled to 18 ℃ saturated state by surface cooler to achieve the effect of cooling and dehumidification. Then, part of the treated air enters the runner for dehumidification treatment, and the other part of the treated air passes through the bypass without dehumidification. These two parts of the treated air are mixed after the runner and sent to the working area through the fan. After such treatment, the outlet temperature of dehumidified air is TN = 29 ℃, RHN = 38%, which fully meets the design requirements and ensures the reliable operation of the unit.

                  According to table 3-1, the proportion of the treated air flow through the runner to the total treated air flow is r = (ie IC)  )/( iD-ic)=(52.6-49.3)/(l55.4-49.3)=3.3/6.1=0.54

                 Therefore, the air volume G1 through the runner is: G1 = R ×  G=0.54 × 10000 = 5400m3 / h. It is known that the air volume of regeneration air is designed to be 1 / 3 of the air volume of treatment air passing through the runner. According to table 3-1, the total cooling capacity Q1 required by the unit is calculated as follows:

          Q1=G × ρ×( iA-iC)/3600+1/3 ×  G1 × ρ×( iL-iM)/3600

          =   ten thousand  × twelve  ×( 159.4-49.3)/3600+1/3  × five thousand and four hundred ×  one point two ×( 159.4-96.3)/3600

          =367+37.9(Kw)

          =404.9(Kw)

          Where ρ Is the air density, take 1.2kg/m3, lower   Same as.

                  According to the refrigeration capacity, condensation temperature and evaporation temperature, the refrigeration compressor can be selected, and the relevant refrigeration components and pipelines can be configured. When selecting a refrigeration compressor, you can choose a compressor with stepless energy regulation or a compressor with stage energy regulation,   Such as 0-25% - 50% - 75% - 100% four stage adjustable compressor, in this example, that is to use such a four stage adjustable compressor. In addition, in order to adjust and control the refrigeration system, the number of condensing fans can be controlled, and the condensing air volume can be controlled by frequency conversion or adjusting valves.

          3.2 electric heating system for treated air

                  The most unfavorable (extreme) environmental meteorological parameters in winter in table 2-1 are taken as the inlet design parameters, that is, TW = - 10 ℃, RHW = 95%.   Through the observation and analysis in L-D, it is not necessary to open the wheel dehumidification system and refrigeration system in winter extreme environmental conditions, but only need to heat the dehumidification air. In the example of this paper, the treatment air is electrically heated to 16 ℃ and the temperature rise of the treatment fan of 1 ℃ is considered. Therefore, it can be seen from the L-D diagram that the temperature TN of the treatment air at the outlet of the dehumidifier is 17 ℃ and the relative humidity RHN is 12.1%, which fully meets the design requirements. The specific parameters of each main processing point are shown in table 3-2.

               

          According to the parameters in table 3-2, the maximum heating quantity Q2 required for dehumidification air in winter is: Q2 = G × ρ×( iB-iA)/3600=10000 ×  one point two ×[ 19.7-(-6.5)]/3600=87.3(KW)

                 Considering the possibility of operation in spring and autumn, especially when the refrigeration compressor is not stepless energy regulation, the heater should be set in front of the surface cooler. In this example, 0-25% - 50% - 75% - 100% staged energy modulation cold compressor is selected, so the heating capacity of heater in front of surface air cooler can be designed as 106kw (the design value is greater than 404.9) × 25 = 101.2kw, and when the heater is fully opened in winter, the outlet temperature of the treated air TN = 20.9 ℃, and the relative humidity RHN = 10%, which meets the design requirements). The heater can be stepless or group controlled. In this example, it is divided into four groups, each group is 26KW.

          3.3 wheel dehumidification system

               At present, the runner specifications are basically uniform, and the diameters are mainly as follows:

          Φ 350mm、 Φ 550mm、 Φ 770mm、 Φ 965mm、 Φ 1050mm、 Φ 1220mm、 Φ 1350mm、 Φ 1525mm、

          Φ 1740mm、 Φ 1940mm、 Φ The thickness of the runner is 2190 mm, mainly 200 mm and 400 mm, but the commonly used runner thickness is 200 mm.

                 In this paper, the design example uses the runner calculation software to calculate the runner selection, and then designs the runner dehumidification system. The selection calculation results are shown in Figure 3-2 [2].

          In the known example, the regeneration air volume is designed as 1 / 3 of the treatment air volume through the wheel dehumidification, and the regeneration temperature is designed as 120 ℃

              The mass velocity VM of the treated air passing through the runner is 3.3kg/m2.s, that is, the surface wind speed V is designed to be 2.75m/s. According to the calculation of 3.1, it is known that the treated air volume G1 through the runner dehumidification is 5400m3 / h

          Regeneration heating capacity:

               Q3=1/3 × G1 ×  p × c ×( tn-tm)/3600=l/3 × five thousand and four hundred × one point two × one point zero one ×( 120-30) / 3600 = 54.5 (kw), where C is the specific heat of air, taking 1.01kj/kg. ℃.

                  According to the above calculation results, you can choose Φ nine hundred and sixty-five × 200 mm silicone runner. The heating capacity of regeneration heater can be designed as 57kw, and stepless adjustment or group adjustment control can be adopted to prevent too high regeneration temperature and burning runner. In this case, the design is divided into three groups, 19kw in each group.

          3.4 electrical control system

                  There are many parameters for unit control and regulation, such as the start-up of refrigeration system and the energy regulation of refrigeration compressor, the start-up number of condensing fans and air volume regulation, the regulation of treatment air heater and regeneration air heater, the regulation of bypass air volume, etc. at present, PLC or Siemens logo is basically used in the design! Control. In this example, logo | control is used, and the main electrical control design is shown in Figure 3-3   Figure 3-4 and figure 3-5 are shown for reference [3].

          4 Summary

                 The shipyard four season air-cooled mobile combined dehumidifier mainly includes refrigeration, runner, electrical control system and mechanical shell

                  4.1 the refrigeration capacity of the unit is generally large, and the stepless or step energy regulating refrigeration compressor is often selected. In addition, the condensing fan system should be able to be auxiliary adjustable, which can be realized by opening the number of condensing fans, adjusting the speed of fans or adjusting the regulating valve installed at the outlet of condensing fans;

                 four  . 2. In order to ensure the good operation of the unit, especially when the refrigeration compressor is not stepless adjustable, the treatment air heater should be set in front of the surface cooler;

                 4.3 in order to protect the runner and prevent it from being burned, the regenerative heater is generally stepless or group controlled, and equipped with high-quality temperature sensor and controller;

                 4.4 the unit has high control requirements and many control parameters. Generally, PLC or Siemens logo is used for logic control, and temperature and humidity sensors are reasonably configured;

                 4.5 the unit operates all the year round. Generally, the refrigeration system and the runner dehumidification system are started in summer, and the air heating system is only started in winter. In spring and autumn, it depends on the specific situation. Therefore, it is necessary to constantly revise and determine the control parameters and adjust the control procedures through practice to ensure the optimal operation of the unit;

                 4.6 the mechanical design of the shell shall be convenient for hoisting and have strong anti-collision ability to adapt to the use environment of the shipyard; In addition, the condensing exhaust air of the refrigeration system can be used as the air source for the runner regeneration in the design, and the non-contact air heat exchanger can be used in the runner regeneration system for the heat exchange between the inlet and outlet air of the regeneration system, so as to reduce the energy consumption of the unit.

          reference

          [1] Lu Yaoqing, et al. Practical heating and air conditioning design manual (Second Edition) [M], Beijing: China Construction Industry Press, 2008.5

          [2] Proflute, procalc2.14 [Z], Sweden: proflute, 2006.3,

          [3] Siemens, logo|   Manual [M], Germany: Siemens company, June 2003,

          [4] Du long, Zhang Weihong, steady state performance simulation analysis of runner and cooling dehumidification combined air conditioning system under off design conditions [J], Nanjing: Journal of Southeast University (NATURAL SCIENCE EDITION), 2005,35 (1): 86 ~ 89

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