Fuzzy control of calcium carbonate and silica scales in geothermal systems

Abstract

Calcium carbonate scaling and silica scaling are critical challenges directly affecting the efficiency of production during operational periods for geothermal power plants or geothermal district heating systems. Although their precipitation mechanisms are different from each other, both can be observed in varied proportions in production and reinjection wells as well as surface equipment in geothermal systems. Thus, scale prevention and control systems are essential, as abatement of scaling is more efficient than removal from wells and equipment after precipitation in a geothermal system. There are a few methods for control of silica and calcium carbonate precipitation in geothermal wells and surface equipment. Most production and reinjection wells require the implementation of a silica/calcium carbonate inhibition system to prevent silica/calcite precipitation inside casings, pipes, separators and other surface equipment in geothermal power systems. Installation of inhibitor systems are the most effective and practical solution for prevention of scaling problems and production loss, if the optimum inhibitor dosages are determined and applied effectively in geothermal systems. Less than optimum ratios of inhibitors may result in product overfeed, increased costs, and in some cases, inhibitor-induced fouling. The system is nonlinear and has multiple dependent and independent variables thus, it is difficult to obtain a mathematical model that describes the relation of geothermal fluid characteristic and inhibitors and with this reason, a fuzzy controller may be good option to resolve it in geothermal systems. Fuzzy control may replace the role of the mathematical model in conservative controllers, substituting it with a different model that is built from a number of smaller rules that only describe a sub-section of the complete system. In this study, two fuzzy logic controllers have been designed to control precipitation of silica and calcium carbonate by using scale inhibitors.