Manifold seals

FIGURE 5.1 Schematics of edge sealing of planar cells (above) and external gas manifold seals (below) used for a simple cross-flow SOFC stack design. 

A large diffusion may be found also for composite materials, carbon, or metal based. In the first case different types of polymeric resins (thermoplastics, such as polypropylene, polyethylene, and PVDF, or thermosettings, such as epoxies and phenolics) are filled with carbonaceous powders (graphite or carbon blacks), to provide a material characterized by very high chemical stability in the fuel cell environment and satisfactory properties of electrical conductivity, but which cannot offer sufficient robustness at thickness lower than 2 mm. The metal composite plates are essentially based on combinations (sandwiches of different layers) of stainless steel, porous graphite, and polycarbonates, with the aim to exploit the characteristics of different materials. Their fabrication can be more complex but this is compensated by the possibility to incorporate other functional components, such as manifolds, seals, and cooling layers. 

Non-repeat components. The components described in the previous section are usually referred to as repeat components since every cell has those components with multiple cells present in a cell stack. Non-repeat components are those that are used only once in a cell stack. The main non-repeat components in a cell stack assembly are pressure plates, coolant inlet and outlet manifolds, reactant inlet and outlet manifolds, and manifold seals. Multiple cells placed between coolers are stacked between two stainless steel pressure plates and loaded axially to arotmd 60 psi with the help of tie rods that run the entire length of the cell stack. Reactant manifolds are then assembled onto the cell stack with manifold seals placed between the cell stack and the manifold. These reactant manifolds are made of stainless steel and coated with PTFE coating to prevent phosphoric acid attack of the manifolds. It is very essential to ensure that there are no pin holes in the PTFE coating for the same reason mentioned above. In phosphoric acid fuel cells, manifold seals made... 

Manifold seals. Most HR system manufacturers employ a flexible tubular seal ring between manifold and nozzle to enhance the guarantee of leak proofing (see Figure 4.82). 

Eig. 20. Cut view of Chlorine Engineers membrane bag cell a, manifold b, frame c, partition plate d, sealing plug e, recirculated NaOH inlet f, cathode g, anode h, cathode can i, membrane bag j, base k, butterfly valve 1, feed brine m, depleted brine n, caustic outlet. 

The cell head is fabricated from a 2.54-cm steel plate and has separate compartments for fluorine and hydrogen. The oudet-gas manifolds, hydrogen fluoride feed and purge lines, and electrical connections are on top of the head. The gas separation skirt is made of Monel. An insulating gasket maintains the seal between the tank and the head. The anode assembly consists of 32 carbon blades bolted onto a copper bar, each of which contains three copper conductor posts. The cathode assembly consists of three vertical, 0.6-cm parallel steep plates. The plates surround the anode assembly and are supported by three steel posts which also serve as conductors. 

Vertical pre.s.sure leaf filters. These filters have vertical, paraUel, rec tangular leaves mounted in an upright cylindrical pressure tank. The leaves usually are of such different widths as to aUowthem to conform to the curvature of the tank and to fill it without waste space. The leaves often rest on a filtrate manifold, the connec tion being sealed by an O ring, so that they can be lifted individuaUy from the top of the fil-... 

Transfer of fluid in a fermentation plant usuallv makes use of air pressure differences. One or more manifold headers may interconnect many vessels. As transfers may have to be aseptic, headers are pressurized with steam until needed. A typical arrangement of steam seals is shown in Fig. 24-12. 

Alternatively, reactant and product gases can be distributed to and removed from individual cells through internal pipes in a design analogous to that of filter presses, (iare must be exercised to assure an even flow distribution between the entiv and exit cells. The seals in internally manifolded stacks are generally not subject to electrical, thermal, and mechanical stresses, but are more numerous than in externally manifolded stacks. 

The bipolar plates are made from either Type 310 or Type 316 stainless steel, which is coated on the fuel side with nickel and aluminized in the seal area around the edge of the plates. Both internally and externally manifolded stacks have been developed. 

Conventional Flare System - The majority of pressure relief valve discharges which must be routed to a closed system are manifolded into a conventional blowdown drum and flare system. The blowdown drum serves to separate liquid and vapor so that the vapor portion can be safely flared, and the separated liquid is pumped to appropriate disposal facilities. The blowdown drum may be of the condensible or noncondensible type, according to the characteristics of the streams entering the system. Selection criteria, as well as the design basis for each type of blowdown drum, are detailed later in this volume. The design of flares, including seal drums and other means of flashback protection, is described later. 

Fignre 9-1 is a schematic drawing of the major eqnipment and protective measnres that comprise the vent manifold system. In the system shown, the vent vapors (offgas) from the condensers of two vacnnm col-nmns are collected in a manifold which goes to the vacnnm pnmp system. From the vacnnm pnmp system, the vapors go to a seal dmm (hydranlic flame arrester), and then to the firebox of a process heater, where they are incinerated. 

Because this design has relatively low power density, recent work has focused on a monolithic SOFC, since this could have faster cell chemistry kinetics. The very high temperatures do, however, present sealing and cracking problems between the electrochemically active area and the gas manifolds. 

The seal tank/pot is not a separator but a physical liquid seal (Figure 7-70) to prevent the possibilities of backflash from the flare from backing into the process manifolds. It is essential for every stack design. 

When a boiler may not be shut down for maintenance of the level control chambers isolating valves can be fitted between the water-level control and the steam space. In this instance, the valves must be capable of being locked in the open position and the key retained by a responsible person. When these valves are closed during maintenance periods the boiler must be under manual attendance. Fitting of these valves should only be with the agreement of the insurance company responsible for the boiler. Drains from the water-level controls and level gauges should be collected at a manifold or sealed tundish before running to the blowdown vessel. 

During the last year we have built an FTMS instrument specifically designed for laser-induced thermal desorption from single-crystal surfaces. Figure 5 is a perspective drawing of the Instrument. The chamber is pumped by a 150 1/s ion pump and has a base pressure of 2.0 X 10- torr. Gases are Introduced through sapphire-sealed leak valves from a diffusion pumped gas manifold. 

The benefits of controlled microwave heating, in particular in conjunction with the use of sealed-vessel systems, are manifold ... 

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