# Designing an industrial dehumidifier

### Case

Manufacturing of lithium batteries takes place in extremely low humidity dry rooms. These size of these rooms may range from small R&D lab environments to large-scale mass production facilities. The reason for maintaining a low humid environment for facilities used for the production of lithium batteries is because such batteries are highly reactive with water vapor. Faced with an even low humidity environment, lithium immediately reacts to form lithium hydroxide, hydrogen, and heat that can finally lead to catastrophic results and endangering the safety of the people working in the production area. The rate of such a reaction highly depends on the humidity of the environment; therefore, an ultra-low humid environment is needed for producing and working in such facilities.

Our company was requested designing an industrial dehumidifier aimed at providing the desired air dew point for a lithium battery production dry room located in Florida.  The dry rooms were adjacent to each other with one having an RH of 5-10 % while the other having an RH of 0.02 % corresponding to a dewpoint of -69 °C.

### Requirements

1. The facility was supposed to be a three room compound with one room for the normal work of the employees while the other two rooms used as laboratories for working on lithium batteries.
2. The humidity density in the main lab was to be 20 ppm (20 water molecules in 1,000,000 air molecules)

### Challenges

The main challenges that we were to resolve were the followings:

1. The large size of the facility
2. Ultra low humidity density of 20 ppm
3. Cost-effectiveness of the final solution

### Solution

The design team considered the environmental condition of the compound as below.

 Ambient Conditions: Temperature/Humidity= 31 °C / 70 % (RH) Room A: Temperature/Humidity= 22 °C / 5- 10 % (RH) Dew Point =  -20 °C Air flow =  3000 kg/h Room B: Temperature/Humidity= 22 °C / 0.02 % (RH) DewPoint=-69°C Air flow = 9000 kg/h

Air to atmosphere:                Temperature / Humidity =  50 °C / 20 % (RH)

Dew Point=  +21 °C

Airflow =  3000 kg/h

The main components of the design included the followings

1. Blowers

The blowers had the following function

• Suction the ambient air
• Provide a positive pressure & recirculation in the Dry rooms A & B
• Deliver the wet air from desiccant wheels regeneration to the atmosphere
1. Four Heat Exchangers

The scope of the heat exchanger was to cool down the dry air to the required temperature

1. Filtration Units

The filtration units were to remove particles and dust coming from the ambient air & from Room A and B. The filtration unit was composed of the Main filter and a Pre-filter

1. An Electrical Heater / Gas burner

The burner consisted of a rust-resistant cast iron body (which served as the gas manifold) drilled to discharge the fuel between the diverging stainless steel mixing plates. The main heater assembly housed the circulating air fan, the gas burner, the fuel gas line and all the necessary safety and burner management system controls.

1. Two desiccant wheels

Implementation of the desiccant wheels was aimed at removing the humidity of the processed air up to a dewpoint of -69 °C. They were the most important part of the unit and a correct selection was made in collaboration with the manufacturer

1. Control system

The control system of the industrial dehumidifier was done by a Programmable Logic Control (PLC).

The main parameters to be controlled were the followings:

• Relative humidity in rooms A & B.
• Dry Airflow to rooms A & B.
• Air changes per hour in rooms A & B.

The above parameters were controlled by adjusting

• The rotation speed of the desiccant wheels
• The rotation speed of the blowers
• The temperature of the regenerated air
##### Description

In order to understand and predict the function of the system, detailed calculations were made to find the behavior of the design at two steps of operation.
1. During the startup
2. During the normal operation
Calculations showed that during the startup stage, once the stable operation conditions were obtained, the dry rooms were ready for the next stage. Under normal operation, an increase of the RH was adjusted automatically by the PLC. PLC was programmed to gradually increase the rotation speed of blowers and based on the condition, it could adjust RH during the operation of the system.
Calculations proved that the design successfully met the requested requirements for 20ppm. Also, through proper choice of system’s different components, we managed to find a very cost-effective solution for making the design.

B. Morrison
April 25, 2018
UK
###### Category:
Mechanical Engineering