Wet sealing

Tapered shaft must be replaced if damaged by wet seal gas or contact with aluminum seal. 

Air-dry samples thoroughly at room temperature, which should not exceed 40°C (loss of Hg ) place the sample on the bag and turn over as necessary. Use gloves Any residual humidity will promote anaerobic reactions, including sulphate reduction, and must be avoided. When samples are properly dried, transfer to a new bag, if necessary (field bag may still be wet), seal and send to LAB IV. 

Jun, J., Jun, J., Kim, K. (2002). Degradation behaviour of Al-Fe coatings in wet-seal area of molten carbonate fuel cells. J. Power Sources 112,153-161. 

Capillary sealing effects are controlled by wetting phenomena which, for hydrocarbons in general, are poorly constrained. In real sub-surface situations, the assumption of a water-wet seal is reasonable for an initially hydrocarbon-free seal. This may be less likely in dynamic situations where capillary seals may leak periodically in the presence of active charge. The wetting properties of seals may change through time an initially water-wet seal may evolve into a hydrocarbon-wet seal, due to the adsorption of a variety of compounds from crude oil, such as asphaltenes (Anderson, 1986). This may ultimately result in a top seal which has no capillary seal capacity and leaks via two-phase flow. 

The strength of the matrix and the electrolyte structure depends on the relative amount of carbonate and LiAlOi. At low carbonate contents, the structure is rigid. Currently, 40 wt%i of L1A102 and 60 wt%i carbonate mixtures are used to form the matrix. At the fuel cell operating temperature, the electrolyte structure is a thick paste, which provides gas seals (called the wet seal) at the edges of the cell. 

To prevent short circuiting between the separator plates the electrolyte matrix made of LiA102 extends to the outer edge of the separator plates. The molten carbonate electrolyte penetrates the matrix tile up to the edges, thus providing the necessary wet seal. This sealing is necessary to take care of small pressure differences (some tens of mbar) between gas chambers and the ambience and also between the fuel and oxidant gas chambers. From this short description of the geometry of the bipolar separator plates, it becomes clear that we have three different situations to take care of if we are to prevent corrosion of the separator plates ... 

The anode gas side, which is highly reducing at the inlet, the cathode gas side, which is oxidising and the special wet seal area, where the plates are covered with a thin continuous electrolyte layer around the edges of the plate, thus providing an electrolytic cell comprising anodic and cathodic areas of adjacent cells. 

The anode wet seal is particularly vulnerable, since this seal will experience the largest oxygen partial pressure difference between the anode gas and the depleted cathode gas on the outside of the stack it will therefore suffer the greatest potential difference. 

To control dosing of the PAE resin to the papermaking system, metering pumps and mini magnetic flow or mass flow meters fabricated from 316L stainless steel and fitted with Teflon or Viton-wetted seals are most preferred. Progressive cavity or centrifugal pumps are preferred because they are low shear and impart less heat to the PAE resin. 

Methane / CO2 Recovery Recover lost gas from venting, flaring, or fugitive sources Flash gas recovery LDAR Compressor wet seal vent recovery... 

Electrolyte loss weakens the gas sealing and shortens cell life. The molten carbonates are very corrosive materials. Since the separator is made of stainless steel, corrosion takes place on the surface of the separator. To reduce the corrosion, the anode side is coated with Ni and the wet seal area with Al. 

According to the report on a 2 MW field test at Santa Clara, the causes and amounts of electrolyte losses are as follows cathode hardware loss, 73% fixed losses, 17% vaporization loss, 7% and unaccounted loss, 3% [7]. The report pointed out that most of the electrolyte loss was due to corrosion at the cathode because the Ni and Al coatings on the anode and wet seal area respectively prevented serious corrosion. Mitsubishi Electric Co. reported that about half of the electrolyte loss was due to the corrosion at the cathode current collector and the loss was proportional to the area of the current collector [8]. 

Trocciola J, Schroll C, Elmore D (1975) Wet seal for liquid electrolyte fuel cells. US Patent 3,867,206, 18 Feb 1975... 

In internal manifolding, the preferred method of sealing is to use the electrolyte matrix itself as a sealant. The electrolyte matrix forms a wet seal in the manifold areas around the gas ducts. In internally manifolded stacks, the entire periphery of the cell may be sealed in this way. It is possible to seal the manifolds with separate gaskets and to extend the matrix only over the active cell area, but this method is rarely used. 

Figure 7.13 Examples of practical separator plate designs with intenal manifolding (a) IMHEX design of ECN, (b) multiple cell stack of Hitachi, and (c) the cross section of the wet-seal area in an internally manifolded MCFC stack.

Shaft seal is used to minimize or elimiitate gas leakage from the contact between casing and shaft into atmosphere. Following shaft seals are available lab)rinth seal, restrictive ring seal, mechanical seal, and liquid film seal. Labyrinth seal is a dry seal. Liquid film seal is a wet seal. The other two can be either dry or wet seal. Interested reader should read reference 4, 5, or 9 for these seals. 

Prevention or at least minimization of fuel and/or oxidant leakage or intermixing of the fuel and oxidant is the most important attribute of an operating fuel cell. An intermixing of fuel and oxidant not only reduces efficiency but can also lead to premature component failure due to excessive local heating. The carbonate fuel cell has successfully adapted a simple wet seal concept. Liquid electrolyte held up in the micro-pores of the matrix and on the metal surface where the metal to matrix interface seal is involved, provide adequate barrier to gas leakage. 

Fig. 11 Wet-seal aluminum protection The coating process reduced the cost significantly while maintaining excellent corrosion resistance.

Cleaned coolant passes through the elanent modules, and past a pressurized wet seal arrangement that eliminates the bypassing of contaminated coolant. Pressurization of the seal with clean coolant ensures that no contaminated coolant is allowed to migrate into the clean coolant section of the filter. The cleaned coolant passes on to the system s clean coolant pump, and thence to the point of use. The filter elements are regenerated by a backflow of clean coolant. 

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