MVM-EGI’s CIRCUMIX^TM hydrodynamic mixer has been developed for the large-scale, continuous production of powder-liquid mixtures. Its patented working method relies on the momentum of flow, hydrodynamic forces, turbulency of the liquid and optimized residence time to produce highly homogenous mixtures rather than mechanical agitation.

CIRCUMIX^TM is available for a wide range of capacity requirements, its rated capacity ranging between 20 and 300 m3/h of continuous mixture production. The density and therefore the concentration of the produced mixture is continuously metered and can be accurately controlled. The mixer can cope with both Newtonian and Bingham-plastic fluids.

CIRCUMIX^TM offers multiple advantages over traditional, mechanically agitated mixers:

• Due to its specially designed shape and working method all the fluid is kept in constant, vigorous motion, there no “dead” zones where particles could settle: the homogeneity of the produced mixture is unusually high.
• With no mechanical agitation and hardly any moving parts, the construction is simple, the equipment is highly reliable, easy to maintain, wear and tear is minimized.
• The continuous operation makes it an ideal candidate for different mixing tasks in the process industries.

3D model of a Circumix^TM mixer 

Pre-assembled Circumix^TM mixer(s) in the workshop before shipment. 

MVM-EGI’s Dense Slurry System for handling coal combustion residues (CCRs) uses Circumix^TM mixers to produce a highly homogenous, dense, pumpable suspension (slurry) of fly ash and water mixture which, upon discharge at the landfill, cures into a solidified product with low-risk environmental properties.

Besides fly ash the mixture can contain inert CCRs such as bottom ash, air preheater/economizer ash and /or flue-gas desulfurization (FGD) gypsum. The water used to create the mixture can be wastewater from the power plant, such as FGD water, cooling tower blowdown or water treatment effluents.

The slurry can be described as a non-Newtonian, Bingham-plastic fluid with water to solid mass ratio ranging typically from 0.8 to 1.2 depending on CCR properties.

DSS offers considerable environmental advantages over other ash handling options, including dry disposal, because its solid end-product has low hydraulic conductivity and exhibits near optimum use of water and reasonable compressive strength:

• No fugitive dust: Neither the closed mixing and transport system, nor the concrete-like solid end product releases dust.
• No soil or ground water pollution. Upon discharge, the slurry solidifies within 24-72 hours and fully cures in about one month. The cured end-product has low hydraulic conductivity, typically in the 10^-6…10^-10 m/s range. This prevents the rainwater ingress and dissolution of pollutants. The leachate of DSS landfills is proven to be clean, free of heavy metals and its volume is low. If collected, returned, and recycled as make-up water for the FGD or the DSS, zero liquid discharge can be achieved.

Excavated part of the DSS landfill well demonstrates the concrete-like nature of the solidified slurry

Farming is safe right next to a DSS disposal site 

• Elimination/reduction of wastewater. The hydrated mineral components of the end-product contain considerable amounts of bound crystalline water.Additional water is captured in the voids of the solidified material and evaporates from the surface of the landfill. Thus, only about 5-15 percent of the transport water is returned as leachate, the rest is sequestered. If wastewater, such as FGD effluent is used to produce the slurry, then water management costs can be significantly reduced.

In terms of O&M costs, DSS is highly competitive to other ash management solutions, especially dry disposal with truck transport.

• As the hydro dynamic mixer has no mechanical agitators, there are hardly any moving parts in the system other than the special, purpose-designed slurry pumps. This ensures high availability, little downtime and reduced O&M costs.
• Due to the optimum slurry viscosity maintained, the wear of the transport pipes is low. 15+ year lifetime is not uncommon.
• A single operator can oversee the automated operation of the system. There is no need for manpower at the disposal site or at the transport system during day-to-day operation.
• Power demand of transport is low due to the optimum slurry concentration.
• There is no need for dust-control measures at the landfill.

The DSS technology has been developed since the mid-1980s and has been successfully applied in several plants in Europe (Hungary, Romania) and in the USA and India. The working references have served more than 6000 MW generating capacity worldwide, some with more than 15 and even 20 years of outstanding operation.

DSS mixer station 

Circumix^TM mixers in operation

DSS can not only serve operating or future coal power plants but can also be instrumental when a coal plant must be shut down as a part of decarbonization efforts.

Decommissioning of a coal plant includes the safe closure of the ash landfills, either in place, or by “clean-closure”, that is by moving the content of the landfill to a new location which complies with today’s environmental standards.

In close-in-place projects DSS can be used to form an isolating cover on the top of the landfill out of the CCRs themselves. This can help maintaining power generation even during the closure projects.

In clean-close projects DSS can be a great tool for admixing stabilizing agents, such as fly ash to the reclaimed material.

Cap of solidified dense slurry over an existing ash deposit 

Closed dense slurry disposal site with a PV plant on the top