Scope and Objectives

Scope : In boilers, hot ash particles impinge on the tubes, causing erosion, simultaneously the salt environment present in the boiler environment also causes high-temperature corrosion. Even the ash and slag build up on the tube surfaces as insulating complex oxides. The fly-ash deposition to heat exchange surfaces is an active target of research due to its negative impact in boiler performances. Serious economic losses are a direct consequence of tube fouling and slagging which reduce the overall boiler efficiency. High temperature corrosion and erosion by the impact of fly ashes and unburned carbon particles are also the main problems to be solved in these applications. The accumulation of material on boiler surfaces can cause overheating and/or corrosion. Both of these conditions frequently result in unscheduled downtime. Furthermore, heat transfer plays a crucial role in boiler efficiency. Slag accumulation and fouling of tubes is quite common during energy production and these factors can significantly decrease heat transfer rates. Since the tubes are continually receiving a lower level of heat, the amount of fuel needed to accomplish the required production must increase as well. Surface coatings prevent the formation of iron oxide, as well as, reduce slagging, thus increasing the heat transfer rate. There is a strong need to develop the suitable coating compositions which have a greater emissivity rate than the tube and facilitate better heat transfer by replacing the iron oxide layer. The material should provide a barrier of protection between the tube surface and the combustion to prevent slag build up. Reduction in slag and tube protection can increase the life of your tubes, as well as lower your fuel consumption needs. Objectives: The main objective of the proposed work is to develop commercial surface coatings to control the erosion-corrosion (E-C) of boilers in coal based thermal power plants. The composition will be such that the coatings will have high hardness, inert to oxides to the extent possible, high bond strength, dense and resistant to slag and fly ash penetration. This project will delve into the deposition mechanisms observed in the field, explore through existing thermodynamic models to identify potential alternative coating solutions, which can work in tandem with design fixes such as soot blowers or ultrasonic horns to vibrate the ash off the tubes.

Deliverables

The project will, upon completion, define the coating material chemistry, feedstock powder / wire size specification, coating process specification, and develop a process plan which is capable of producing coatings with the desired thickness, integrity and overall performance characteristics. The combination of ash-phobicity, good heat transfer characteristics coupled with high temperature erosion and corrosion resistance can result in breakthrough gains in boiler efficiency and reliability. Such coatings are not available off the shelf. The capability of these coating offerings in terms of durability and in terms of reducing heat rates will be the key deliverable. The industries involved in power generation and boiler fabrication shall be major beneficiaries. IIT Ropar and GE have expertise in the field of corrosion science and coatings. The synergy between IIT Ropar and GE will result in advanced coating systems that will improve power plant performance and reliability. Indian power market is mostly based on thermal energy and current ash-phobic solutions are either inadequate or very high in cost. The aim of the project will be to deliver a solution that is effective and at the same time low cost

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Scientific Output

1. Production of nickel chrome-based coatings 2. Understanding of coating process parameters for performance at high temperature 3. Initial development of relationship between ash phobic ability and coating composition 4. Generation of database based on performance of coatings in actual boiler conditions 5. Analysis and characterization of fly ash formed from various coals

Results and outcome till date

The fly ash received from GE Power was characterized. It was observed that small particles agglomerate to form bigger particles. The coating compositions based on NiCr with addition of WCCoCr, Si, Zr and TiC have been blended successfully. P91 boiler tubes were grit blasted and coated with these compositions. The coated samples have been characterized using SEM/EDS and XRD. The coating were found to be intact and displayed uniform distribution of blended powders. The presence of all the elements was confirmed using EDS and XRD facility.

Societal benefit and impact anticipated

Our research would decrease the downtime and operating costs of the boilers, which in turn can reduce the per unit production cost of the electricity.This may reflect as reduction in electricity bill.

Next steps

The coated samples will now be tested for 1. Metallurgical properties 2. High temperature erosion corrosion resistance 3. Ash phobic properties 4. Heat transfer ability The tested samples will further be characterized to understand performance of the coated samples and failure mechanism in under performing coating.

Publications and reports

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Patents

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Scholars and Project Staff

1 SRF joined on 23 october, 2017

Challenges faced

The equipment to measure thermal conductivity was also required to be purchased. The allotted amount was less than the requirement and hence the PI had to arrange money from other sources to fund the purchase of equipment which resulted in spending considerable time during first year of project.

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