CONTROLLED OZONE GAS RECYCLING IN AN OZONE PULP BLEACHING PROCESS

摘要

A method for controlling the gas recycle loop of an ozone bleaching process wherein an ozone generator produces an ozone containing gas from an oxygen containing feed gas and delivers the ozone containing gas to an ozone reactor at a variable flow rate responsive to reactor ozone demand. Pulp is bleached with the ozone containing gas, thereby producing an exhaust gas having a flow rate that varies in response to the flow rate of the ozone containing gas delivered to the ozone reactor. The exhaust gas is then recovered and its flow rate is modified within the recycle loop so that an amount equivalent to reactor ozone demand is returned to the ozone generators. The oxygen content of the oxygen containing feed gas is monitored at or near the inlet of the ozone generator and an amount of fresh oxygen is supplied to the oxygen containing feed gas to obtain a predetermined level of oxygen therein. Additionally, an amount of exhaust gas may be purged at a rate substantially equivalent to the rate fresh oxygen is supplied. However, the pressure at the ozone generator is also monitored and the purge rate is adjusted in order to maintain constant pressure at the ozone generator.