Supercritical boiler design pdf

A short summary of this paper. McCauley D. Kraft M. Maryamchik D. Wietzke K. Barberton, Ohio, U. McCauley, D. Kraft, M. Maryamchik, D.

The primary stage is an impact finally to the introduction of circulating fluid beds, techni- solids separator located at the furnace exit which collects cal advances have met the ever changing needs of industry. The Modern grate stoker technology is used successfully today primary separation stage is arranged as an array of water- for waste-to-energy power plants, and BFB technology is cooled, segmented, U-shaped vertical elements U-beams.

With three-years of successful commer- Likewise, the circulating fluid-bed CFB combustion cial operation, the latest IR-CFB design is being expanded process has been a market-wide success. The development of the CFB technology Scale-up to to MWe, with higher steam tempera- has evolved over the past three decades. The latest efforts tures, increases these efficiencies and benefits.

This allows are focused on developing large capacity, supercritical once- for a highly competitive utility-scale power plant for central through CFB boilers for utility electric power generation.

Pilot-scale operations The drivers for these scale-up efforts include the need for are currently underway to finalize the design of an advanced higher plant efficiencies firing waste coal, low volatile an- IR-CFB that will utilize in-bed heat exchangers IBHX.

Current results of the pilot testing and boiler de- bustion process to transfer heat from the chemical process signs will be discussed, along with applicability to various to the boiler water-cooled tube enclosure and other heating markets throughout Asia. A closed condensing cycle provides enhanced efficiency, as it also allows for close control of water chemistry required for high pressure, high temperature cycles, and favors a mini- mum of makeup water.

An additional improvement is the use of regenerative feedwater heating, which uses extraction steam from various stages in the turbine to heat the feedwater as it is pumped from the condenser to the economizer. Cycle thermodynamic efficiency is improved by increas- ing the temperature of the heat source for a constant heat sink temperature. This temperature can be increased when the feedwater pressure is increased because the boiler inlet pressure sets the saturation temperature in the Rankine cycle see Figure 2.

If the pressure is increased above the critical point of bar psi , the addition of heat no longer results in a typical boiling process in which there is defined interface between the steam and water.

Rather, the fluid can be treated as a single phase. This is referred to as a super- Fig. The principally and to prevent agglomeration of the solids. In general, with equivalent plant parameters the reduction of sulfur dioxide SO2 by adding limestone fuel type, heat sink temperature, etc. In addition, The majority of the solids attempting to exit the furnace there are constraints imposed by the economics of fuel selec- are captured and returned within the furnace enclosure.

PGG design provides recycling of a minor solids stream from a multi-cyclone dust collector MDC located in the convection pass; however, this solid stream is quite small Bubbling fluid-bed technology compared to the solids collected by the U-beam separators. The BFB combustion process has been successfully ap- The MDC impacts the upper furnace heat transfer rate, and plied in smaller industrial boiler applications see Figure 3. In smaller, lower velocity beds, the surface can be arranged to eliminate the Supercritical steam cycle history need for complicated tube supports.

The process is carried out reversibly since available. The coal feed was simply fed into the lower furnace bed using a chute, and the higher fluidizing velocities typical of the CFB process effectively mixed the coal, bed material and air.

There were no in-bed tube bundles to erode. The CFB process carried the solids to the vertical furnace enclosure walls to transfer the heat. High solids circulation rates allow uniform furnace temperature.

Without in-bed tube bundles, supports, and their inherent maintenance, were not required. The primary separator is arranged as an array of U-shaped vertical elements U-beams. The secondary separation stage, typically an MDC, is located in the lower gas temperature region of the boiler convection pass, i.

The U-beam separator design has evolved through several generations see Figure 4 , starting with 11 rows installed Fig. While each U-beam in earlier designs was made of biomass fuels, and many BFB industrial projects have as a single piece supported from the top, the current design been successful for many years. The work during the first ten years was limited to studies and pilot-scale testing.

Between the late s and mid s, two demonstration facilities were built, and three commercial installations were built. However, there were three significant lessons with the utility size application of the BFB combus- tion process: 1. The coal distribution was difficult for large or multiple beds. The coal was injected into the bottom of the bed with under-bed pneumatic systems. These systems plugged and eroded and the availability of the system was limited.

The beds had in-bed surface to control the bed tempera- ture. The surface was generating surface that utilized forced or pumped circulation and final superheater surface. These tube bundle surfaces eroded over time due to the erosive impact of the bed material.

Tube sec- tions had to be replaced in 5 to 10 years of operation. The tube bundles required support. The tube supports were uncooled and typically operated at C F. The first supports required constant maintenance which affected availability. Later, the tube supports were increased in mass and mechanically tied together no welds , which proved to be more successful, but quite expensive. Higher solids collection efficiency helps to achieve greater inventory of fine circulating particles in the furnace that provides: a higher furnace heat transfer rate, b better control of furnace temperature, and c better carbon and sorbent utilization due to the increased residence time of fine particles.

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We look forward to hearing from you. Renewable Overview. Thermal Overview. Company Overview. Home Supercritical Boilers. Specific advantages include: For a given output, lower fuel consumption, and thus lower carbon emissions, than other less efficient systems The load change rate capability of the system is not restricted by the turbine Steam temperature at the inlet and outlet of the reheater is nearly constant over a wide load range The boiler feedwater pump power is significantly reduced at lower loads Short startup times Higher plant efficiency over the entire load range.

Rapid Startup Systems. In this case, a drum-type boiler is used because the steam needs to be separated from water in the drum of the boiler before it is superheated and led into the turbine. Water Phase Diagram Once-through through boilers are therefore used in supercritical cycles. A critical point can be illustrated on a Rankine cycle, on which a typical steam turbine power plant operates. At working pressures in excess excess of this critical pressure, the Rankine cycle becomes supercritical cycle.

The region below critical point is the subcritical region having a non-homogeneous homogeneous mixture of water and steam. Figure-2 Figure 2 shows the supercritical Rankine cycle.

Based on the operating pressures, there are two basic boiler technologies employed in the modern coal-fired coal power plants. These are Subcritical and Supercritical Subcritical boilers operate below bars, the supercritical pressure of water.

This means that there is a non non- homogeneous mixture of water and steam in the evaporator part of the boiler. In this case a drumdrum-type boiler is used because the steam needs to be separated from water before it is superheated and led into the turbine.

The remaining water in the drum re-enters enters the boiler for further conversion to steam. The water circulation system can be a natural circulation or a forced assisted circulation circulation.

Up to Nickel-based Nickel based alloys, e. This corresponds to The minimum constant pr. The start-up and re-circulation system is designed to provide the necessary mass flow for adequate cooling of the evaporator during start-up and low load operation. In this re-circulation system, the feedwater flows through the boiler feedwater line to the economizer, to the evaporator and then to the water separator.

From the separator the recirculated water returns through the Boiler Recirculation Pump to the boiler feedwater line, where it is mixed with feedwater. Efficiency calculation of boiler: There are two methods to calculate the efficiency of boiler. That is, Heat loss method and heat input- output method.