Freezing products

摘要

A method of freezing a product, which method comprises the steps of warming nitrogen in indirect heat exchange with a product to the frozen, work expanding said nitrogen, and using the expanded nitrogen thus obtained to refrigerate the or another product. Liquid nitrogen is pumped (11) from a storage vessel (10) through a heat exchanger (12) to an expander (16). The expander may drive an alternator connected to an electric heating element used to heat water. The expander may drive a turbulence inducing fan. The liquid nitrogen coming from the pump may be passed through a common header to a number of heat exchangers connected in parallel.