The IR-CFB boiler-based captive power plant helps a cement manufacturer improve his profit lines while remaining environmentally friendly, says Vivek Taneja.

When business organisations consider moving to decisions that are sustainable – like saving electricity, recycling water or using renewable energy – the big investments required upfront would certainly impact the balance sheet here and now. However, if we were to think of a longer time-frame, all these decisions would make a lot of sense when we consider the concept of lifecycle cost – a higher capital cost, but with far lower operating costs such that it pays for itself over the life of the product. Long-term sustainability also goes hand- in- hand with the kind of decisions we make, processes we follow, policies we adopt and the values we propagate. Companies passionate about the cause of sustainable development will constantly come up with innovative solutions which, over time, will definitely add to the bottomline. If we were to redefine the success of an organisation as achieving the triple bottomline – economic, environmental and social – it would be a sustainable model and also benefit the bottomlines of the company in the long run.

In today’s competitive scenario, it is imperative for any cement manufacturer to maintain his growth and keep all shareholders happy, but at the same time, improve his profitability by improving the plant’s specific energy consumption, while remaining committed to the environment by reducing his carbon footprint. An Internal Recirculation – Circulating Fluidised Bed (IR-CFB) boiler-based captive power plant distinctively helps a cement manufacturer meet these objectives and improve his competitive positioning.

An IR-CFB is a compact boiler, with various unique features to ensure minimum maintenance, thus offering the maximum available uptime for the power plant. The design incorporates a two- stage separation system for better bed inventory control. The benefits of this patented technology include a superior combustion efficiency, high operational thermal efficiency, low emissions, low maintenance, low pressure drop, and a high turndown, resulting in an improved overall plant performance. The two-stage system includes a primary U-beam impact separator and a secondary multi-cyclone dust collector (MDC), which work together to provide a combined particle collection efficiency in excess of 99.8 per cent. The U-beams, a staggered array of stainless steel channels at the furnace exit plane, capture nearly all the solids suspended in the flue gas leaving the furnace, and internally re-circulate these solids to the lower furnace. The ceramic MDC, with small diameter 250 mm cyclones, captures the solids in the second pass and returns this material to the lower furnace in a controlled manner. The ability to regulate the secondary recycle system provides the operator with an unprecedented furnace temperature control, resulting in improved boiler performance and relatively faster load response.

Compact and simplified This two-stage particle separation system results in a compact, simplified boiler arrangement. The entire U-beam particle separator is located at the furnace exit. Compared with hot cyclone-type CFBC designs, the IR-CFBC has significantly lower furnace exit gas velocity and requires significantly less building volume. By relying on internal recirculation, the IR-CFBC design eliminates J-valves, loop seals, high-pressure blowers, and soot blowers, which are required with other CFBC designs. One goal of CFBC boiler manufacturers has been to eliminate thick, un-cooled refractory and hot expansion joints from their designs to reduce the expense and lost time associated with refractory maintenance. This goal was achieved with the development of the IR-CFBC boiler. The furnace, U-beam separator, and super-heater enclosures are constructed entirely of top-supported, gas-tight, all-welded membrane tube walls, which do not require hot expansion joints. The small amount of refractory that is used in the IR-CFBC is applied to selected areas of the water-cooled enclosure surface in a thin layer which is only 16 mm thick in the lower furnace and slightly thicker over the tube face elsewhere in the furnace. As a result, IR-CFBC requires only 10 to 25 per cent of the total refractory found in a hot cyclone CFBC design and less than 50 per cent of the refractory used in a water-cooled or steam-cooled cyclone CFBC unit. This construction has significantly reduced the need for refractory maintenance in operating CFBC units.

The patented reduced diameter zone (RDZ) tube section is another feature designed to reduce maintenance. The RDZ consists of a reduced diameter tube section mating to a specially-shaped ceramic tile. The reduced diameter tube section on each tube slopes away from the solids falling down the wall. This eliminates the solids material from building up and eroding the furnace tubes where the lower furnace refractory ends.

Erosion is a major cause of maintenance problems in CFBC boilers due to the high solids loading in the flue gas. The severity of this erosion is exponentially related to the velocity of the flue gas through the system. On hot cyclone CFBCs, the particle separator depends upon an extremely high flue gas velocity to provide the energy needed to efficiently disengage the particles from the flue gas. By comparison, the U-beam particle separator is designed to operate efficiently with much lower flue gas velocity at full-load operating conditions. The particle capture efficiency actually increases as the flue gas velocity through the U-beam separator decreases. By operating at such a low gas velocity, the potential for erosion in the IR-CFBC is significantly reduced. Proper material selection and low flue gas velocities allow reducing the erosion of U-beam separators, thus reducing the maintenance down time throughout years of operation at design load conditions.

Another advantage of IR-CFBC technology is that it allows the owner to specify a wide variety of fuels to optimise the profitability of the facility. Different type of fuels that can be successfully fired into an IR-CFB boiler include Indian or imported coal, lignite, petroleum coke (petcoke), washery rejects, mill rejects, agro-waste, biomass, char, etc. Other fuels such as fly ash and sludge are also candidates, depending on their percentage of heat input, moisture content and emission requirements. The IR-CFB boiler also can be designed to burn several of these specified fuels in the same unit. This provides an additional flexibility needed to respond to changes in the fuel markets.

Environmentally friendly

The design also ensures best-in-class compliance with environmental norms. The IR-CFBC boiler can control SO2 emissions by injecting limestone into the lower furnace. Relatively low NOx emissions are inherent in the IR-CFBC due to low and uniform furnace temperatures and staged combustion. NOx emissions can be further reduced by using a selective non-catalytic reduction (SNCR) system. In addition, the IR-CFBC’s patented secondary particle recycle system provides increased control, not found in other CFBC technologies, to maintain an optimum uniform furnace temperature which is essential for low SO2 and NOx emissions and for better limestone utilization.

Thus, for energy intensive sector like cement, an Internal Recirculation – Circulating Fluidised Bed (IR-CFB) boiler- based captive power plant guarantees to the cement manufacturer an improvement of his profitline as well as a reduced carbon footprint. For these organisations not in the power business, the retention of highly experienced and dedicated team of resources to set up and operate captive power plants is a challenge not related to his core business, thus exposing the business to unwanted risks. These include risks related to cost and time overruns, integration hurdles between various packages, project management to take care of unforeseen risks, ensuring quality to address issues related to reliability and availability of power from the power plant. This is where the cement industry can benefit from the services of an experienced EPCOM (Engineer-Procure-Construct-Operate- Maintain) contractor who will guarantee performance and the overall completion schedule within fixed costs. The contractor will also guarantee reliable power at the least lifecycle cost because the entire risk of operating and maintaining the power project is also outsourced to this experienced service provider.

However, it is very important that the project developer must look for the following abilities while finalising an EPC contractor:

• Is the EPC company willing to take single- point responsibility for executing the project? This will ensure that the entire set of risks associated with the power project is effectively transferred to the EPC contractor, with matching securities, ensuring peace of mind for the developer.
• Does the EPC company have a successful track record of executing similar types of challenging projects? This is necessary to ensure that the contractor can incorporate its learning from executing similar projects and deliver optimised solutions that would ensure minimum lifetime costs for the power project.
• Does the EPC company have the financial strength to wade through the entire lifecycle of project execution?
• Is the contractor aware of the local legal issues that must be adhered to, to ensure the smooth execution of the project?
• Is the contractor a manufacturer of the key equipment that would be used in the power project? This will ensure that the contractor has a greater control over the project schedule.
• Does the contractor provide after sales service? If the contractor also offers Operation and Maintenance (O&M) services after setting up the power plant, it would ensure minimum investment for the developer into resources for managing the power plant, thus enabling him to maximise his profits.

An EPC company that satisfies these criterions will ensure that all the risks associated with the project are identified up-front and are mitigated at the earliest to ensure on- time implementation of the project, thus providing a win – win situation for both the developer as well as the solution provider.

Vivek Taneja, Head Business Development-Power Division, Thermax Email – vtaneja@thermaxindia.com