background
A large coal handling and preparation plant in New South Wales was having problems with scale build-up in their process water piping, spray bars and reverse osmosis membranes. This is a common challenge in coal handling facilities; washing coal, which contains sulphides, results in acidic, low pH wash water. The client had been applying hydrated lime as a cheap solution for pH correction which has the affect of causing problematic scale within all piping, pumps, valves, sprayers, etc.
The client contacted WTS to identify the cause of their scale problems, then develop & implement a solution, with consideration given to compatibility with the infrastructure’s chemistry limitations and cost efficiency.
solution
The scale control technology WTS-4-1100 was developed. This technology, now available for tailoring to similar situations, was a bespoke formulation for this customer’s specific circumstances. WTS-4-1100 is a blend of a phosphonate and various polymers which act as crystal modifiers, threshold inhibitors and dispersants.
The WTS-4-1100 treatment comprises three main components to target calcium and sulphate based scales:
- a phosphonate to act as a crystal modifier
- a polymer for dispersion and scale inhibition and
- a copolymer with high calcium tolerance to stabilise the formulation
advantages
- Effective. Against the major forms of scale.
- Reliability. Reduced scale reduces likelihood of blockages and breakdowns
- Operational efficiency. Scale-free systems operate as intended
- Low adsorption into coal – better scale protection and coal performance
- Protects. against corrosion of plant’s infrastructure
- Easy to use. Single product liquid formulation
- Cost effective. Bespoke solution targeted to achieve requirements using least product at lowest cost
WTS’ approach
Water samples were taken and the plant’s water handling infrastructure analysed to understand the water to be treated and the constraints the solution had to comply with. Cation/Anion analysis of the water/wash chemistries showed typically high levels of sulphates and chlorides in an alkaline environment.
WTS’ software modelling technology was used to explore various proposed solutions over a range of pH and temperature conditions. The modelling calculated saturation levels for Ca, Mg, Ba and Sr. These were graphed for the corresponding scale potential for the inorganic salts, CaCO3, SrCO3, MgCO3 and BaSO4.
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| Selection of graphs for scale forming salt saturation points over pH and temperature ranges | ||
Coal, being highly adsorbent, can limit the efficacy of many chemicals, so WTS performed polymer adsorption tests on coal fine slurries with different solution formulations. For the final formula, it was observed that 60-70% of the polymer remained available & effective at dose rates of just 30-50ppm. This allowed better solution dosage modelling and thus accurate cost-benefit calculations.
A selection of formulas were considered and modelled at varying concentrations. Some were more effective than others, but the modelling showed their efficacy as scale inhibitors was comparable for the degree of scale control required for this case. This allowed WTS to select the most cost-effective solution for the client.
conclusion
WTS 4-1100 technology, tailored and carefully applied to individual applications using WTS’ software modelling technology, offers a wide treatment range which covers the day-to-day fluctuations in plant operating conditions. This effective formulation offers a plethora of reliability, corrosion protection and cost benefits as well as being an excellent scale inhibitor
The careful blend of scale inhibitor materials and their targeted application provides a synergy more effective than the individual ingredients. This combination increases the scope of the application to allow for a more versatile range of working conditions such as pH, temperature, water purity and hydrodynamic operations where the product is effective. This versatility also extends to affecting a wide range of the major inorganic salts responsible for mineral scale formation.
