ABSTRACT

Water scarcity and environmental issues have necessitated operating cooling systems using poor quality feedwaters or changing process temperature conditions. Safety concerns have driven cooling system users to implement alkaline treatment programs to facilitate acid feed reduction or elimination. Inorganic and/or organic phosphorus components in alkaline cooling water treatment (CWT) programs help prevent corrosion and scale formation. Collectively, water conservation measures and alkaline CWT programs have increased potential metal-phosphate and/or metal-phosphonate scale formation. Understanding deposit control polymers (DCP) perform under stressed conditions is essential for implementing alkaline CWT programs. This paper discusses CWT program metal-phosphate/phosphonate scale formation control efficacy when operating under stressed alkaline conditions (e.g., high temperatures, suspended solids, and iron).

INTRODUCTION

Industrial water systems operated using poorly treated feed water are often plagued by undesirable deposits on equipment surfaces.1 These deposits can be categorized into the following five groups: (a) mineral scales, (b) corrosion products, (c) suspended matter, (d) microbiological mass, and (e) other (e.g., oil grease, formulation component hardness ions salts). These deposits typically accumulate in low- flow circulation areas and may become immobilized during upset conditions resulting in build-up on heat exchanger and equipment surfaces. Among the various strategies adopted to retard or prevent undesired deposits is the use of chemical additives that inhibit nucleation and crystal growth, disperse precipitated salts, and/or particulate matter. Developing cost-effective deposit control solutions is a dynamic challenge.

Effective cooling water treatment (CWT) programs must control scale, corrosion, particulate matter, and microbiological growth. CWT program evolution includes acid/chromate, zinc/chromate, stabilized phosphate, alkaline CWT programs, such as phosphonate/zinc/polymer, and all-organic. Stabilized phosphate formulations typically require acid feed to maintain a neutral pH. Alkaline CWT programs (e.g., all-organic) can minimize or eliminate acid feed. Most formulations contain one or more phosphonate (e.g., 1-hydroxyethylidine 1,1-diphosphonic acid [HEDP], 2-phosphonobutane 1,2,4- tricarboxylic acid [PBTC]) for CaCO3 inhibition and mild steel corrosion control. High performance DCPs are essential components for neutral pH and alkaline CWT programs. DCPs serve dual functions: (1) control calcium phosphate (Ca/P) and calcium phosphonate formation on metal surface and (2) disperse recirculating water suspended solids minimizing potential deposition on system surfaces.

This content is only available via PDF.
You can access this article if you purchase or spend a download.