A top of the range A-grade boiler could have as much as 96 per cent efficiency
Greenesol Power Systems is one of the leading equipment suppliers for cement companies. Shridhar Nambi, Director and CEO, Greenesol Power Systems, explains how to get the best from boilers, critical equipment in manufacturing facilities. Excerpts from the interview.
What is the range of boiler technologies offered?
We have a very wide range in boilers in terms of capacity ranging from 10 mw to 500 mw and fuel flexibility with systems running on coal, bio mass, bagasse, natural gas, waste heat recovery.
Which are the latest innovations in boiler design?
The latest in the market is the new boiler master concept, which combines the benefits of throttle pressure firing (return to the throttle pressure set point) and drum pressure firing (dynamic stability). It consists of a throttle pressure controller (reset action plus feed-forward signal) working in parallel with a drum pressure controller (proportional and derivative action). Since they are separated in the time domain, the controllers do not interact. This approach has proven particularly effective at stabilising the operation of boilers equipped with low-NOX burners.
The new arrangement is much more stable than traditional throttle pressure firing. It has been successfully deployed on several units and should be of great interest to owners of subcritical coal-fired units because it offers a quick and inexpensive solution to pressure stability problems.
How does drum pressure compares with throttle pressure for boiler control?
Drum pressure is far superior to throttle pressure as a boiler control index. Drum pressure, as a function of energy balance, is represented by a first-order lag, whereas throttle pressure is represented by a third-order lag.
A standard proportional-integral-derivative algorithm cannot execute its derivative function properly on a third-order process feedback variable such as throttle pressure.
Drum pressure reacts more quickly than throttle pressure to changes in heat input, in some cases up to 45 seconds faster. Faster feedback improves control loop stability. Since drum pressure reacts faster, using it for feedback improves boiler stability. Changes in drum pressure are linear, with respect to changes in energy balance.
There's a good reason why most boilers are still fired by throttle pressure: Throttle pressure is the final, visible product. It is what impacts steam turbine performance. Drum pressure is an intermediate result; the control system has to be stable and maintain throttle pressure as constant as possible.
What are the major factors that reduce boiler lifecycle and reliability?
Boiler tube failures remain a leading behind the breakdown in power boilers. The need for strategic planning with regards to inspections, preventative maintenance and targeted replacements is great. Identifying where and how to begin a boiler management program can be viewed as an insurmountable obstacle by many utility operators and owners. In addition, the cookie-cutter approach established in many cases results in poor reliability improvement due to specific operating and design conditions is not identified and evaluated. Each boiler has its own unique operational history and condition. To improve a boiler's reliability, it is imperative to consider the boiler's unique conditions and develop a strategic plan to improve safety and reliability.
What are the challenges for companies in boiler design and manufacture?
Depending on where they are located on the production circle, companies should prioritise four broad areas for resource productivity: production, product design, value recovery, and supply-circle management.
Most manufacturers have already made tremendous gains by implementing programmes to improve labour and capital productivity, for example, through lean manufacturing. Such efforts can improve resource productivity if they are adapted to include criteria for reducing the consumption of energy and raw materials. Here we focus on energy, a particular concern for upstream manufacturers, since energy costs can account for as much as 20 per cent of their overall production costs. Manufacturers can take four steps to increase energy productivity. Companies can adapt methodology for lean-value-add identification to map energy consumption at every step of their operating processes. This will enable them to calculate the thermodynamically minimum energy required and evaluate actual consumption relative to this theoretical limit (an approach known as pinch analysis). The analysis reveals where energy is wasted and how losses can be avoided.
One US surfactant maker that conducted a heat-value-add analysis found that only 10 per cent of its steam-heat inputs were thermo-dynamically required to make its products; 90 per cent were wasted. The manufacturer implemented about 20 measures and captured steam savings worth 30 percent of its baseline energy costs, enabling it to recoup what it invested to launch the effort within three years. One measure, which involved implementing a new software algorithm to control the company's heating and cooling control loop, enabled it to reduce its need for steam by 5 per cent.
Moving beyond pinch analysis, companies can extend their lean programmes to improve energy efficiency by optimising energy integration in heating and cooling operations. For instance, one chemical company changed its process to release heat more quickly during polymerisation, allowing evaporation to start sooner, thus reducing the energy it used in the subsequent drying stage by 10 per cent.
Companies can use lean approaches to identify process-design and equipment changes that can deliver greater energy efficiency. One Chinese steel mill saved 8 million renminbi (about $1.2 million) annually by lowering the levelling bar in a coke furnace an extra few centimetres, which reduced the mill's total energy cost by 0.4 percent. The mill achieved an additional 5 million renminbi ($730,000) in annual savings by adding an insulation layer to ladles used in steelmaking.
Lean-energy approaches can eliminate waste and capture savings by optimising the interface between producers-for example, steam-boiler operators, cooling-water-unit operators, and power suppliersùand consumers. One chemical plant managed to avoid a $2 million investment to increase its boiler capacity by improving consumption planning-specifically, ensuring that demand would not pass the threshold that triggered pressure drops during demand spikes.
By incorporating energy and materials parameters into their product-design approaches, companies could reduce the use of materials that are hazardous, non-renewable, difficult to source, or expensive. Changes to product design could increase opportunities for recycling and reusing components and materials at the end of a product's life cycle. And designers could prioritise the incorporation of sustainable features into their products to reduce the impact products have on the environment. These principles constitute a philosophy known as circular design, which extends beyond products to systems and business models.
Companies that take these steps could reduce costs and facilitate compliance with regulations while bolstering their reputation and building relationships with consumers and other stakeholders. Additionally, they can often expand existing design to cost methodologies to quantify the financial or brand impact of incorporating sustainable features in their products.
Where do customers usually go wrong while picking up the right boiler technology?
Choosing the right boiler can be complicated. As well as the costs involved, you have to consider the type that works it needed.
All new boilers must now be high-efficiency condensing boilers unless it is too difficult to fit one. Condensing boilers capture the heat that is normally lost by traditional boilers and reuses it. This means that a top of the range A-grade boiler could have as much as 96 per cent efficiency.