Water contains various types and amounts of impurities which can vary with the source of supply and its geographical location. Impurities present in water can be classified as dissolved solids, dissolved gases and suspended matter. Water dissolves gases from the air as well as gases produced from organics in the soil. It picks up suspended matter from the earth. Water is also subject to contamination by industrial wastes, oils and process materials. As a result, both chemical and mechanical means are needed to treat water and make it of acceptable quality for use in boilers. This is the primary purpose of the pretreatment system.

The pretreatment system is the most critical part of the total boiler system with respect to maintaining boiler cleanliness. Here, water impurities are either removed or reduced to acceptable levels for a particular boiler operation. The system incorporates various combinations of processes:

• * Cold Lime Softening
• * Hot Lime Softening
• * Filtration
• * Zeolite Softening
• * Demineralization
• * Dealkalization
• * Reverse-Osmosis

The processes and the equipment within the process depend entirely on the type of raw water to be treated and the particular use for the treated water (e.g., boiler make-up water).

The goal of a pretreatment system is to produce water of acceptable quality for use in the boiler. This means that the equipment in the pretreatment system must function as the manufacturer intended. And, if it is to function properly, the equipment must be controlled and understood by all personnel involved. Whatever is done in the pretreatment system directly affects the operations of the boiler.

A system that is not controlled properly can result in many problems. Lack of control, resulting in excessive leakage of hardness salts, silica, metallic ions or oxygen to the boiler feedwater, causes scale or corrosion in the boiler or increased corrosion in the condensate system. Scale and corrosion occur because the chemical program in use is designed to control these contaminants at their normal controlled levels. The internal chemical program can be adjusted for minor fluctuations in the boiler make-up water quality; however, when large fluctuations occur, it cannot be expected to keep the boiler system free from deposits and corrosion.

Finally, the deposits formed in the boiler cause overheating, loss of efficiency, higher energy costs, and eventually, tube failures. These tube failures lead to a very serious situation: excessive mechanical repair with loss of production. In more serious situations, injury to personnel, and even death, could result. So, to prevent the ultimate loss of plant production, to ensure personnel safety and for proper functioning of the internal chemical program, the pretreatment system must be controlled and maintained in proper working order.