JACKETED TANKS AND THERMAL SHOCK

Jacketed tanks/reactors are commonplace in the chemical industry. Many batch operations in the chemical industry require both heating and cooling at different times in the process. Rapid changes in temperature of the heat transfer media can thermally shock the equipment. Typically, thermal shock is defined as changing the cooling or heating media at the jacket inlet more than 25 F per minute. Thermal shock can be avoided by tempering the heat transfer media and providing proper venting. Tempering is easiest achieved when a common heat transfer media is used for both heating and cooling. A Temperature Control Unit (TCU) can be used to adjust the temperature of the heat transfer media at a rate that does not pose the risk of thermal shock. While TCUs are the simplest means of controlling temperature and protecting equipment many companies still insist on using different media for heating and cooling. Many times this includes steam heat and water cooling. If this MUST be done some minimum precautions should be taken.

1. HEATING to COOLING:

When changing from steam heating to cooling water one of the following procedures should be followed:

A. Forced Tempering

Vent steam out of jacket and drain condensate. Allow jacket cool down naturally or use compressed air to blow-down the jacket from top to bottom to achieve correct temperatures. Close vents and slowly introduce hot water at the correct temperature to the jacket. Increase flow rate to process conditions and decrease water temperature at a rate of less than 25 F per minute.

B. Natural Tempering

Vent steam out of jackets and completely drain all condensate. Allow the jacket to cool down naturally to the correct temperature. Close vents and introduce cooling water.

2. COOLING to HEATING:

When changing from cooling water to steam heating one of the following procedures should be followed:

A. Forced Tempering

Raise circulating water temperature in the jacket at a rate of less than 25 F per minute until desired steam temperature is reached. Vent jackets and completely drain out water. Close vents and slowly introduce steam into the jacket.

B. Natural Tempering

Vent and drain water out of jackets. Let the jacket warm up naturally to the correct temperature. Slowly introduce steam into jackets at reduced pressure and/or flow rate (temperature) until the desired steam temperature is reached. As with any manual process, there are risks associated with this.