Common Scale Minerals

Numerous types of scale have been reported to date. In most cases, they include one of these components within their structures: carbon, magnesium, calcium, aluminum, silicate, organic matters. However, the formation of these scales is a critical problem encountered in many industries including water transport, oil or gas production, and power generation.  

Calcite and struvite are two most common scale minerals. As these scale minerals grow within pipes, they reduce the diameter of the pipes and threaten flow assurance. For calcite scale, once it builds up on the metallic surfaces of heat transferring facilities, such as heat exchangers or boiler tubes, both the performance and heat efficiency of these systems are substantially lowered as well as increasing the operational costs due to the increase in its thickness as more and more fuel energy is required . According to one research data, just one eighth of an inch of scale reduces heating efficiency by 25%, leading to wasted energy and financial resources. It is also very expensive to remove, as de-scaling pipes and boilers alone costs huge dollar amount each year.

Struvite Scale

Struvite is a phosphate mineral frequently encountered in livestock waste management systems. At waste treatment plants, a large volume of struvite scale (magnesium ammonium phosphate: MAP) is frequently deposited on pipe walls and equipment surfaces of sludge treatment systems, causing it to plug and damage pipes, pumping units, aerators, screens, belt presses and other operation units. As a consequence, struvite accumulation has rendered extensive piping systems inoperable and has required a continuous maintenance for removing struvite from equipment operating in post-digestion sludge storage basins. 

Previous research of struvite formation often focused on cleaning by acid or recycling systems after struvite deposition. In spite of numerous attempts and investigations to solve this puzzle, a fully desirable control of struvite scales has remained unsolved. Most methods introduced to the markets appear to pose their advantages and disadvantages. Most remediation methods turned out to be often either impractical or very costly in terms of labor, materials, and system downtime. Most methods to prevent or remove struvite deposits from anaerobic digestor and post-digenstion pipe walls were not often fully successful and, in some cases, the replacement of entire piping system was suggested as one of the troubleshooting methods. 

Below listed are the collection of some selected articles or reports dealing with struvite issumes. Click them to see details.

            - Struvite

            - Struvite Control in Wastewater

            - Struvite Scale Formation And Inhibition In Wastewater

            - Control of Struvite Deposition in Wastewater Treatment Plants

            - Chemical Control of Struvite Precipitation

            - A Struvite Control and Phosphorous Removal Process For Centrate 

            - Pilot-scale struvite recovery from anaerobic digester supernatant 

            - Water and Wastewater Q&A regading Help Forums

            - The Equipment To Remove Nitrogen and Phosphate using the Struvite Crystallization

Calcite Scale

Calcite, a common undesirable scale-forming mineral, occurs as a main ingredient of chalk, limestone and marble. While infilterating through these rocks, water dissolves calcite and become calcium-rich hard water. This hard water subsequently precipitates it out to form a very hard scale. Calcite deposits form numerous layers rimming pipes, jets and equipment, and totally block in the event.

Calcite is often deposited onto the surface of heat transferring units and oilfield production wells. The development of calcite scale is a multistage process and is affected by a number of factors such as supersaturation ratio, bicarbonate ion concentration, temperature, flow velocity, and pH of ambient fluids. Calcite scale also actively precipitates in areas of frequent pressure change and turbulence, such as pipes and pumps. It often causes substantial problems for technical applications, increasing pressure losses and decreasing flow rates. 

The deposits reduce heat transfer in heat exchangers and lower the efficiency of the heating installation/cooling system quite significantly. Water containing 145 ppm of calcite, flowing at 3.5 litres per minute, produces in one year 4.8 kilograms of scale at 60ºC. At 80ºC this rises dramatically to a massive 29.9 kilograms! In oil fields, the formation of such calicte scale may causes severe production decline rates and/or substantially extended pump run times in wells. In some cases, pump failures may occur due to blockage of perforations and reduction of the internal diameters of tubulars.

Numerous studies have been carried out to learn about controling and reducing common and serious engineering problems derived from the build of calcite scale in pipes or machines. Calcite scale problems can be ameliorated by chemical, physical or biological methods with various level of effectiveness. These controls can be grouped into three main categories: methods by solubility control, methods by altering the growth mechanism of crystals, and methods by changing the potential of a surface to foul. Although each of these scale-controlling methods has their advantages, environmentally friendly and safe options utilizing ultrasonic devices such as Morko USP will become prevalent eventually in the near future. 

            - Calcium scale

            - Calcium carbonate 

            - Calcium carbonate scale control, effect of material and inhibitors

            - Solving the scaling problem

            - Lime scale

            - Effect of ultrasonic field on calcium carbonate scale formation  

            - Calcium Carbonate Scale in Oilfield Operations

            - Calcium Carbonate Scale Control in Industrial Water Systems

            - Fouling Problem

            - Controlling Scale Deposition and Industrial Fouling