FLY ASH CONVERSION - A PRACTICAL PATH TO PRODUCING ZERO CARBON CEMENT AND IMPROVING THE BENEFICIATED USE OF FLY ASH...
Powder River Basin (PRB) coal burned at high temperature generates a fly ash, classified as Class C, which can be used directly as the base solids material in CeraTech's high performance cements. This is due to the fact that the PRB coal contains high levels of calcium that are converted into a reactive fly ash generating a hydraulic or cementitious reaction when combined with CeraTech's proprietary liquid additives. The fly ash requires no additional manufacturing, processing, or refining. It can be taken directly from the coal-fired power plants and shipped to ready-mix batch plants or precast plants.
The high calcium PRB coal is prevalent in the United States, but not in the rest of the world where coal is more often bituminous or sub-bituminous lignite. Most coal sources throughout the world have much lower levels of calcium. As such, most of the fly ash generated Internationally is not suitable for CeraTech's cement technology. For the past several years, CeraTech has actively researched and tested the feasibility of converting a non-reactive Class F fly ash to a reactive ash with the same hydraulic characteristics as Class C ashes ("Conversion").
The Conversion process is surprisingly straightforward: Calcium is introduced into the coal prior to combustion. While simple in theory, it is more challenging in practice as (i) subscale laboratory tests are inadequate (boilers used for laboratory testing typically do not reach the same temperatures and combustion profile as production boilers in coal-fired power plants) and (ii) utilities are universally (and understandably) concerned about any modification to the combustion step.
Full scale testing in China
In recognition of the importance of conducting full scale testing, CeraTech focused its efforts on defining and deploying the conversion test program at a power plant operating in a full production environment. CeraTech recently conducted two conversion program tests, one in March '15 and one in May '15, at the Reiming Power Station in Guan Zhou, China.
The critical objectives of the fly ash conversion program addressed key plant operations, emissions considerations, and the feasibility of effectively converting the fly ash into a reactive glass structure meeting CeraTech's performance requirements for CERATECH™ Cement.
A more detailed description of the objectives is broken down into two areas:
- Operational Feasibility: Demonstrate that calcium can be introduced into the boiler combustion process
- Manage the introduction of a calcium-based addition to the coal stream prior to combustion during full production without any negative impacts to the boiler operations or to combustion efficiency.
- Ensure that co-combusting the combined materials results in either a neutral or positive impact on SOx and NOx emissions levels.
- Conversion Process Effectiveness
- Verify that CeraTech's process can change the glass structure of the fly ash during combustion.
- Verify that the resultant glass contains the targeted levels of increased calcium necessary to qualify as a reactive ash with the same hydraulic characteristics as Class C fly ash used in CeraTech's cement technology.
- Produce a cementitious material meeting CeraTech's performance requirements for CERATECH™ Cement.
Based on our first and second tests conducted at the Reiming Power plant in Guanzhou, China, the conversion program was a solid success. Two independent authorities conducted the testing and analyses, the first in China by Professor Zhou at Xijiang University and the second in the U.S. by the EPIC Research Center at the University of North Carolina in Charlotte.
- The introduction of low levels of calcium had no noticeable negative effects on the boiler (e.g. slagging, fouling).
- There was also a dramatic reduction in SOx emissions of greater than 35%.
- Through XRD and XRF analysis, it was confirmed that the conversion program created the modified, calcium-enhanced fly ash necessary for CeraTech's cement technology.
- The fly ash was of much higher quality and produced a hydraulic reaction. With the addition of CeraTech's proprietary liquid additives, the fly ash had self-cementing properties.
The implication is that through this conversion process, CeraTech can enable power plants to readily produce a beneficiated fly ash that can be immediately used as a zero carbon cement, thus eliminating the need to landfill, dramatically reducing SOx emissions, and mitigating regulatory and environmental exposure all without adversely affecting boiler performance or combustion efficiency.
The other important, consequential benefit is that the enhanced Class C fly ash, due to its cementitious qualities, provides better performance when used in conventional portland cement concrete.