Design, modeling, and optimization of shell and tube exchangers in the thermal network of greenhouse effluent treatment

Document Type : Research Paper

Authors

1 Department of Agro-Technology Engineering, College of Abouraihan, University of Tehran, Tehran, Iran.

2 Department of Biosystem Mechanics Engineering, Faculty of Agriculture, Tarbiat Modares University, Tehran, Iran.

Abstract

Due to the increase in freshwater demand and climatic threats such as the drought phenomenon, it is necessary to implement efficient methods in water and wastewater treatment. Therefore, it is very vital to provide solutions in the agricultural sector and related industries as the largest water consumer in the world. In this regard, the desalination of greenhouse effluent and its reuse by relying on different energy sources can be considered a big step towards the sustainable development of the agricultural industry. Shell and tube exchangers are widely used in various industries. This research is focused on design, simulation, and optimization of four exchangers connected together in the wastewater treatment network of a greenhouse with an area of 2000 m2 located in Tehran using HYSYS and EDR software. One of the advantages of this method compared to reverse osmosis is that it reduces pollution of the environment and water sources. Among the innovations of this research is the use of thermal methods in the agricultural industry. The obtained result shows that the first converter with a square arrangement includes 37 tubes with a length of 1650 mm, the second converter with a square arrangement includes 52 tubes with a length of 1850 mm, the third converter with a triangular arrangement includes 24 tubes with a length of 1700 mm, and the fourth with a square arrangement consisting of 24 tubes with a length of 800 mm. The network is optimal, and 160 L/h of freshwater are delivered to the greenhouse.

Keywords

Main Subjects

Design, Modeling, and Optimization of Shell and Tube Exchangers in the Thermal Network of Greenhouse Effluent Treatment

EXTENDED ABSTRACT

 

Goal

This study was carried out to reuse production effluent in a greenhouse to provide part of the greenhouse's water needs, as well as to prevent the phenomenon of soil salinity and preserve the health of the environment. For this purpose, the design, simulation, and optimization of shell and tube exchangers in the thermal network (series) were done to purify (thermal method) greenhouse effluent. The primary objective is to acquire and design the best possible thermal network of interconnected converters for the treatment of effluent produced in a greenhouse within an area of 2000 m2 located in Tehran Province.

Research Method

The effluent treatment cycle produced in the greenhouse was designed and simulated using HYSYS software. Also, the design, simulation, and optimization of shell and tube exchangers in the effluent treatment thermal network were carried out using EDR software. This software uses TEMA and ASME standards to design the two main thermal and mechanical parts of nodes.

Findings

The results showed that the design of thermal nodes is influenced by several factors. In order to increase the temperature of the intermediate fluid from 25 to 135 °C with a flow rate of 120 kg/h, 87.52 kW of energy is needed in the first cycle of the process and 67.43 kW of energy in the other cycles. Therefore, the difference in energy consumption between the first cycle and the other cycles is about 23%. In order for the thermal power of the first node to be proportional to the power of the heat source, the ideal amount of effluent distribution for the first and second nodes is 110 and 63 kg/h, respectively. Therefore, the power of the first thermal node was 67.9 kW. On the other hand, due to the fact that the first thermal node is the energy source of the second thermal node and also because the amount of effluent in the second thermal node is less than the first thermal node, the power of the second node was 40.1 kW. Despite the lower input flow in the second node compared to the first node, the special conditions of stress in the shell of the second node have led to a change in the geometry and an increase in the weight of the second converter. On the other hand, the decrease of 3 kg in the flow rate of the third node compared to the second node caused the power of the third node to be in the range of the power of the second node, and it was equal to 38.2 kW. The power of the cooler to reduce the water temperature from 80.35 to 47.34 °C from the second cycle onwards, according to the results, is 30.73 kW. For this reason, according to the principle of energy conservation, the power of the fourth thermal node was 7.8 kW. Also, the results showed that the share of consumables in the construction of heat exchangers is between 13 and 18%, and the share of labor wages is 82% of the total cost. Also, the results showed that in the 90° arrangement, the pressure drop and heat transfer reduction are significantly higher than in the 30° arrangement. With the presence of sediment depositing fluid in the shell of the first, second, and fourth nodes, the use of a 90° arrangement is more optimal from the point of view of the economy (repair and maintenance), and with the design and optimization done, the pressure drop and thermal performance were compensated to an acceptable level.

Conclusions

The results showed that only one cycle with four thermal nodes is needed for the desalination of the effluent for each greenhouse with any area. In the proposed cycle, energy consumption is optimal, and it is possible to supply it from renewable sources. The results showed that the optimization of the exchangers led to the economicization of wastewater treatment by the thermal method. The complete compliance of the heating network with the functional, design, and construction criteria of the TEMA standard is proof of quality and compliance with the highest levels of international standards in this field. These requirements include efficiency, heat transfer coefficient, pressure drop, resistance to corrosion, and deposition.

 

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Iranian Journal of Biosystems Engineering
Volume 54, Issue 4
January 2024
Pages 19-28

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History

  • Receive Date: 29 April 2024
  • Revise Date: 20 June 2024
  • Accept Date: 13 July 2024

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