Redundant Programmable Controllers Help Meet Challenging Environmental Law Requirements, 1997 Process Control, Electrical & Info. Conference Proceedings

The proposed Occupational Safety and Health Administration (OSHA) guidelines for safety practices in the process industries, introduced September 11, 1991, and revised in 1992, have been finalized and were due to be fully mandated in 1996. This existing standard addresses a global spectrum of process hazards.

The U.S. Environmental Protection Agency (EPA) has issued an expanded proposed list of hazardous chemicals in 1994. This list, was finalized, and has expanded ten-fold the previous list of proposed hazardous chemicals. The original focus for the guidelines was primarily chemical manufacturers and handlers: the large producers who use automated processes and critical processes. Targeted users now include those industries having one or more included process hazards.

For the pulp and paper industry, the process hazards include a host of items: boiler controls and management systems, power generation gas and steam turbines, chlorine dioxide generators, bleach- handling equipment, large paper machine rotating equipment, and others. Pollution avoidance of air, land, and water resources are at issue.

This paper describes existing redundant controller technologies for meeting safety, environmental, and economic concerns, which will benefit employees, government, the public, users, and producers. Citing an application of redundant high availability PLC systems at McMillam Bloedel Ltd., Powel River Division, British Columbia, will be the primary focus. The mill produces 40,000 gpm of process wastewater which must be treated before it is discharged. The wasterwater comes from various mill plant processes, including pulping, log processing, and papermaking.