Introduction

A peripheral understanding of water is essential for any boiler engineer. The aim of this chapter is to provide such a simplified overview.

Both water and steam tend to dissolve some amounts of material they come in contact with, forming oxides, hydroxides, hydrates, and hydrogen. To protect the equipment, it is essential that water chemistry is controlled. This is done in two stages. Water is first subjected to treatment to make it suitable for admitting into the boiler. In the second stage, its dissolved gases are removed and it is turned alkaline as required to convert it into feed water (FW). In its passage from FW to boiler water and thereafter to steam, water is conditioned suitably by dosing various chemicals at appropriate places to pre­vent it from (1) forming scales, (2) causing corrosion, and (3) contaminating steam.

Water conditioning takes place within the boiler island, and naturally, it is what con­cerns the boiler engineer most. The engineering aspects are given greater stress, with water chemistry as the backdrop.

Boiler failures due to water have substantially reduced over time because of the use of superior water chemicals and better processes, and also because of much deeper under­standing of water-boiler interfaces. Simultaneously, the guidelines evolved with the con­sensus of various interested groups, such as the users, manufacturers, and independent bodies, for the FW and drum water limits for different types of boilers operating at various pressures have greatly simplified water chemistry. If the suggested water limits are prop­erly maintained, pressure part failure is rare.

The responsibility of the boilermakers is to provide the guidelines for FW and boiler water in line with the steam purity requirements of the turbine maker, taking into account the materials of construction and heat fluxes. The duty of the station chemist is to procure a suitable plant and evolve appropriate conditioning as demanded by the power station or process plant.