Seven Years of Successful Operation for Ceramic Filter ( FF 2004)

A ceramic filter has logged seven years of successful operation on a 235-MWe IGCC plant in Buggenum in The Netherlands. Steffen Heidenreich (Pall Schumacher GmbH) and Carlo Wolters (Nuon Power Buggenum BV) described the installation in Filtration+Separation.

The Nuon Power IGCC plant uses a process developed by Shell. Pulverized coal is gasified at 1500° C under a pressure of 28 bar using pure oxygen. The syngas is cleaned after passing through a gas cooler, where the heat in the gas is converted into steam. The steam is then used to drive the steam turbine. Larger flyash particles are collected in a cyclone and returned to the gasifier. The smaller particles are removed from the syngas in a subsequent ceramic hot gas filter system.

The ceramic hot gas filter unit was designed, manufactured and further developed by Pall Schumacher, working in close cooperation with Shell Global Solutions. The filter is equipped with more than 800 Dia-Schumalith ceramic filter candles. The filter candles are arranged in groups. The filter is operated at a temperature of 250-285° C and under a pressure of approximately 26 bar.

The hot gas filter is designed with a venturi head above each group of filter elements for reinforcement of the blowback pressure. The venturi design enables simultaneous cleaning of all filter elements in a group with one reverse pulse, which reduces the required number of jet-pulse valves.

The ceramic Dia-Schumalith filter elements are based on ceramically bonded silicon carbide. The macroporous silicon carbide matrix functions as a rigid, stable structure supporting the membrane, which acts as the actual barrier filter. The membrane consists of mullite grains and has a thickness of 100-200 µm and a pore size of approximately 10 µm.

Since startup in 1994 Pall Schumacher has changed the type of filter elements used because of advances in the technology. The most significant change was made in 1997 by replacing the Dia-Schumalith F-40 filter elements (membrane consists of ceramic fibers) with Dia-Schumalith 10-20 filter elements (membrane consists of ceramic grains).

The main advantages of the change were improved filtration efficiency because of the reduction in the membrane pore size from 15 µm to 10 µm, and better cleaning of the elements because of a smoother outside surface and thinner element wall, i.e., a reduction from 15 mm to 10 mm. The residual pressure drop was also significantly reduced on a long-term basis with the Dia-Schumalith 10-20.

Five Years of Successful Operation for IGCC Filter

Schumacher’s hot gas filter has long-term operating experience in the Nuon Power Buggenum IGCC Power Plant. In Buggenum in the Netherlands one of the world's largest coal gasification plants for electricity generation, a 253-MWe IGCC power plant, was built and started up in 1994. Since 1998, after a demonstration period of three years, the plant has been used as a full commercial electricity generating unit.

Using the Shell process, pulverized coal is gasified at 1500° C and a pressure of 28 bar using pure oxygen. The gas is cleaned after passing a gas cooler. Larger flyash particles are collected in a cyclone and the finer ones in a subsequent ceramic hot gas filter.

The Hot Gas Filter unit has been completely engineered and delivered by Pall Schumacher. The scope of supply comprised the filter vessel with all internals including tube sheet, ceramic filter elements, grid and raw gas distribution system.

The Hot Gas Filter design is based on the Pall Schumacher modular tube sheet configuration. A single master tube sheet contains 18 smaller modular tube sheets. Each modular tube sheet is equipped with a venturi head for enhanced blow back pressure during the cleaning cycle. The Venturi-design enables simultaneous cleaning of 48 filter elements with one reverse pulse which reduces the number of jet-pulse valves to an economical minimum. The Hot Gas Filter itself is approximately 17 meters high with an inner diameter of 4.2 meters and an empty weight of approximately 90 metric tons. The typical construction of the Pall Schumacher Hot Gas Filter design including main parts is shown in Figure 1.

FIGURE 1 Typical PALL SCHUMACHER Hot Gas Filter Design in Principal

The Dia-Schumalith ceramic filter elements are manufactured at Pall Schumacher in Crailsheim, Germany. All Dia-Schumalith filter elements are based on ceramically bonded silicon carbide. The macroporous silicon carbide matrix functions as a rigid, stable structure supporting the membrane which acts as the actual barrier filter. This membrane consists of Mullite grains and has a thickness of about 100-200 µm with a pore size of about 10 µm.

Since startup, the type of filter elements used has changed due to new and improved developments by Pall Schumacher. The most significant change has been made by replacing Dia-Schumalith F-40 by Dia-Schumalith 10-20 filter elements in 1997. Main advantages of the exchange were an improved filtration efficiency caused by reduction of the membrane pore size from approximately 15 to 10 µm, better cleaning of the elements based on a smoother outside surface, and a reduction of the element wall thickness from 15 to 10 mm. The residual pressure drop, on a long-term basis, is significantly lower for Dia-Schumalith 10-20 compared to Dia-Schumalith F-40.Simultaneous with these advantageous changes in filter elements, improved filter element fixturing has been achieved through the installation of a bottom retaining grid. The advantage of the grid is prevention of element deflection thereby increasing the robustness of the total filter element fixture system.

The filter has been in operation for the last five years for about 25,000 operating hours without any measurable dust load on the clean gas side and without any filter element blocking. Different ceramic filter element types have been used. The close cooperation between Pall Schumacher and Nuon Power Buggenum has resulted in the development of a final, well-performing version.

Offline cleaning method of the filter elements offers the advantage for Nuon to save expenditures for new sets of filter elements.

Additionally, the construction of filter and filter element has been continuously improved to perform to customers' needs.

The ceramic filter element lifetime is improved to more than 10,000 operating hours and the current set of elements has been in continuous operation for more than 15,000 hours.

The lifetime of the elements and the delta p development is sufficient to fulfill Nuon's needs to operate the filter unit for 2 years of uninterrupted operation.

There is no need for a previously-undertaken yearly filter overhaul. Therefore, the availability of the total filter plant is tremendously increased.

Schumacher Develops Integrated Fail Safe System ( FF 2002)

Schumacher Umwelt- und Trenntechnik GmbH has developed and manufactured ceramic hot gas filter elements for many years. The first generation of membranes was based on ceramic fibers, while the improved second generation is based on ceramic grains. Some of Schumacher’s latest developments are reported in Filtration & Separation.

Schumacher has recently developed a new hot gas filter element called Dia-Schumalith N. It is based on silicon carbide similar to its well proven Dia-Schumalith filter elements, but has a new binder system offering higher mechanical strength, higher thermal stability, improved corrosion resistance and improved creep resistance at higher temperatures.

Several of the new Dia-Schumalith N elements were tested for more than 1000 hours at a filtration temperature of 850°C within a radioactive waste incinerator. This test was so successful that after the end of the test the complete filter system, which is comprised of 200 elements, was equipped with new Dia-Schumalith N elements.

One potential risk of ceramic filter elements is that they can break when subjected to high mechanical stresses that can occur when process problems arise. To overcome the potential risk of an unscheduled, costly shutdown of the process, a fail-safe system for ceramic filters is desirable. In conventional filter systems, jet pulses are used to clean the filter elements. The integration of a fail-safe system on the clean gas side is impractical when the traditional jet pulse cleaning system is used because introducing a fail-safe system between the pulse system and the filter element would severely restrict the cleaning gas flow, and therefore drastically reduce cleaning efficiency. Jet pulse cleaning systems are also compromised when the filter is dealing with high contents of very fine particles or "sticky" particles.

In order to integrate a fail-safe system and to improve cleaning efficiency, Schumacher has developed an innovative cleaning method called Coupled Pressure Pulse (CPP) cleaning. Figure 1 shows the basis of the new cleaning method, in which the cleaning system is directly coupled to the filter candles. One feature of this new technique is that the cleaning gas pressure exceeds the system pressure by only 0.05-0.1 MPa, whereas in the case of conventional jet pulse systems, double the system pressure (at least 0.6 MPa) is standard. The key advantage of CPP cleaning is that a safety filter for each filter candle can be integrated on the clean gas side. The integrated safety filter ensures continuous operation of the filter system even in the event of damages to the ceramic filter elements, preventing the need for an unscheduled shutdown of the system.

FIGURE 1  Operating Scheme of The CPP Cleaning System, with Integrated Fail-Safe System

A prototype of the new filter system was built as part of a pyrolysis pilot plant at the Karlsruhe Research Centre in Germany. The filter is equipped with six Dia-Schumalith T 10-20 filter candles, each with a length of 1500 mm. Newly-developed individual safety filters were integrated between each of the primary filter candles and the clean gas vessel. For on-line cleaning, the filter candles were arranged in two clusters of three candles each. The operating temperature of the filter was designed to be 550°C.

A pyrolysis process was chosen for the tests as pyrolysis dust is well known as a sticky dust, with a critical filtration behavior. Thus, the CPP filter system could be evaluated operating with one of the most difficult contaminants to remove from the membrane surface.

Initial test runs with the pyrolysis plant have already been conducted, and longer term testing is scheduled for the near future.