Method for controlling an ozone bleaching process

Claim 1

A method for controlling an ozone gas recycle loop in an ozone bleaching process wherein an ozone generator produces an ozone containing gas from an oxygen containing feed gas and delivers said ozone containing gas to a plug flow reactor at a variable flow rate for reaction with pulp, the method comprising the steps of: determining ozone demand of said plug flow reactor based on pulp condition and flow rate; varying the flow rate of said ozone containing gas to said reactor in response to said ozone demand; bleaching the pulp in the reactor with said ozone containing gas, thereby producing an exhaust gas containing contaminants including carbon dioxide, said exhaust gas having a flow rate that varies in response to the flow rate of the ozone containing gas to the ozone reactor; recovering said exhaust gas and returning said gas to the ozone generator to form an ozone gas recycle loop; modifying the flow rate of said exhaust gas into and within said recycle loop so that the flow rate of the exhaust gas returned to the ozone generator substantially conforms to the ozone demand of said reactor; providing a dryer system in said recycled loop to remove moisture from said exhaust, gas: maintaining a predetermined constant pressure at said dryer system in response to the reactor demand; detecting a change from the constant predetermined pressure at the dryer system caused by the adjustment of flow through the bypass loop of the compressor; adjusting a pressure control valve downstream from the dryer system to return the pressure at the dryer system to its predetermined value; monitoring the oxygen content of the oxygen containing feed gas at or near the inlet of the ozone generator; supplying an amount of fresh oxygen to the oxygen containing feed gas at a rate sufficient to obtain said predetermined oxygen composition; purging an amount of exhaust gas at a rate substantially equivalent to the rate of fresh oxygen supplied; detecting a change in pressure at the ozone generator from a constant predetermined pressure caused by the adjustment of flow through the pressure control valve downstream of the dryer system; and adjusting the purge rate in order to maintain constant pressure at the ozone generator; wherein said step of modifying the flow rate of said exhaust gas into and within said recycle loop includes the steps of providing a compressor in said recycle loop, and maintaining a predetermined constant pressure at the compressor inlet in response to the varying flow rate of said exhaust gas by diverting a variable portion of the compressor output back to the compressor inlet.

Claim 2

A method for controlling an ozone gas recycle loop in an ozone bleaching process wherein an ozone generator produces an ozone containing gas from an oxygen containing feed gas and delivers said ozone containing gas to a plug flow reactor at a variable flow rate for reaction with pulp, the method comprising the steps of: determining ozone demand of said plug flow reactor based on pulp condition and flow rate; varying the flow rate of said ozone containing gas to said reactor in response to said ozone demand; bleaching the pulp in the reactor with said ozone containing gas, thereby producing an exhaust gas containing contaminants including carbon dioxide, said exhaust gas having a flow rate that varies in response to the flow rate of the ozone containing gas to the ozone reactor; recovering said exhaust gas and returning said gas to the ozone generator to form an ozone gas recycle loop; modifying the flow rate of said exhaust gas into and within said recycle loop so that the flow rate of the exhaust gas returned to the ozone generator substantially conforms to the ozone demand of said reactor; providing a dryer system in said recycled loop to remove moisture from said exhaust, gas: maintaining a predetermined constant pressure at said dryer system in response to the reactor demand; detecting a change from the constant predetermined pressure at the dryer system caused by the adjustment of flow through the bypass loop of the compressor; adjusting a pressure control valve downstream from the dryer system to return the pressure at the dryer system to its predetermined value; monitoring the oxygen content of the oxygen containing feed gas at or near the inlet of the ozone generator; supplying an amount of fresh oxygen to the oxygen containing feed gas at a rate sufficient to obtain said predetermined oxygen composition; purging an amount of exhaust gas at a rate substantially equivalent to the rate of fresh oxygen supplied; detecting a change in pressure at the ozone generator from a constant predetermined pressure caused by the adjustment of flow through the pressure control valve downstream of the dryer system; and adjusting the purge rate in order to maintain constant pressure at the ozone generator; wherein said step of modifying the flow rate of said exhaust gas into and within said recycle loop includes the steps of providing a compressor in said recycle loop, and maintaining a predetermined constant pressure at the compressor inlet in response to the varying flow rate of said exhaust gas by diverting a variable portion of the compressor output back to the compressor inlet.