Submarines a Comparison, AIP - Fuel Cell or IHD - AIP


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AIP – Fuel Cell or IHD – AIP



Potential Fuel Cell Power Plants & The IHD-AIP Alternative
(Stirling Cycle Power Plants Not Addressed Due To Limitations In Power Density)AIP-

Phosphoric Acid Fuel Cells (PAFC)
Molten Carbonate Fuel Cells (MCFC)
General Observation

Integrated Hydraulic Diesel - Air Independent Power (IHD-AIP) Plant


Potential Fuel Cell Power Plants & The IHD-AIP Alternative
(Stirling Cycle Power Plants Not Addressed Due To Limitations In Power Density)

Through-out this address, IHD-AIP is considered to be an address of an “Integrated Hydraulic Diesel - Air Independent Power Plant” operating in a Re-Cycle Diesel Mode and the following is an operational comparison with what are currently considered, potentially, the two most powerful forms of Fuel Cell.

Although there are great expectations for fuel cell power plants in AIP submarines, as typified by the Russian-made submarines equipped with the Kristall electrochemical generator (fuel cell) AIP plant; as yet there is little real progress towards the availability of such fuel cells in the MW (continuous) range, suitable for use as AIP plant in submarines. There is little to promote the expectation this circumstance will change in the near future.

Irrespective of there currently being in operation a number of existing civil fuel cell generator systems, with an acknowledged operational capacity in the MW range, these have for the most part been basically experimental power plants, with the greater portion of these systems being Phosphoric Acid Fuel Cells (PAFC). In parallel with this, development of Molten Carbonate Fuel Cells (MCFC) likewise holds promise, although as things currently stand, neither of these types is yet well suited to use as a submarine power plant.


Phosphoric Acid Fuel Cells (PAFC)

In the case of PAFCs, the American DoD has for some time now, been operating a number of sub-MW land units as supplemental power plants on various military bases, principally to gain operational data on the type. These units appear to be almost exclusively PAFC type systems and of modest power capabilities. As long ago as the early eighties, PAFC systems were built in the United States with 7.5 MW and 11 MW capacities. With the former subsequently sold to interests in Japan, where it and a lesser 4.8 MW unit of Japanese manufacture, were still in operation, well into the mid-nineties. Not with standing these long-term demonstrations of the viability of PAFC units, in ostensibly civil applications and the demonstrated tolerance of impurities in both fuels and oxidants. Although the PAFC type has a notable operational history, as above, they are never the less, not well suited to submarine applications for a number of technical reasons, including:
· a corrosive electrolyte operating at elevated temperatures with a requirement for demanding storage facilities,
· solidification of the electrolyte at room temperature, in combination with a hygroscopic disposition,
protracted and slow warm through requirements on start-up and demanding cool-down procedures on shut-down,
· the combination of a high operating temperature and corrosive electrolyte results in the use of materials that are brittle and susceptible to shock damage,
· the elevated operational temperatures required for good power densities, is conducive to the phosphoric acid corroding carbon catalyst support and similarly damaging graphic bi-polar plates, whist the catalyst also suffers degradation during operation

There are also a number of individually minor, shipboard environmental liabilities that likewise reduce the viability of PAFC to use as AIP submarine power plants. These include contamination of product water and minor vapor diffusion to the atmosphere. Although power densities of PAFC, in general, is unremarkable, the more compact versions of the type would be acceptable as AIP units, were it not for the sum of the minor disadvantages associated with the type.

Molten Carbonate Fuel Cells (MCFC)

MCFCs have been demonstrated to at least 1.8 MW and with their very high operational temperatures, provide an ability to use internal reforming, when operating on directly introduced vaporous methanol fuel; resulting in reductions in heat, fuel and oxidant losses along with the electrical consumption usually associated with an external reformer, purification, discharge and recycle systems. Total system electrical generation efficiency is, as a consequence, potentially very close to the actual fuel cell efficiency and arguably higher than an equivalent Proton Exchange Membrane Fuel Cell (PEMFC) system. The problems associated with warm-through and cool down cycles are consistent with PAFCs, with the proviso that delinquent temperature control will not adversely effect the platinum catalyst’s performance.

Unfortunately, the use of methanol as a fuel invokes a number of significant penalties. When considering vessels with equivalent MCFC-AIP operational ranges, the first using diesel fuel and the second methanol, the diesel-fuelled vessel has a requirement for approximately 60%, by weight, of the fuel and oxidant of the methanol powered vessel. Given the current projections for MCFC systems, it is unlikely such power plants will result in a single power plant type vessel and as such, a diesel power plant is likely to continue as a major element of this type. If a dual fuel system and the resulting complexity is not to be the result, this will likewise dictate the use of diesel fuelled MCFC.

However, when operating on diesel fuel, the ability to rely on internal reforming must be forgone, in order to prevent soot formation and subsequent contamination problems. In such circumstances, an external reformer is a requirement, further resulting in a requirement to then use sulphur free diesel fuel. However, with the acceptability of carbon monoxide as a fuel component, there is no requirement for a low temperature shift stage to overcome what would otherwise constitute a contaminant in lower temperature fuel cell systems, running on hydrogen reformed from diesel fuel. Although MCFCs have a reduced level of requirement for external reformers, the requirement for sulphur free diesel when operating on diesel fuel as the consumable, represents quite a notable limitation, with regards the integration of an AIP submarine powered by a MCFC into an existing fleet, as it constitutes a requirement for an additional fuel type. This will, of necessity, result in a duplicate and dedicated shore-side storage and bunkering systems, to eliminate the potential for accidental cross-contamination with sulphurous fuels used in alternative applications.

The sum of the above, tends to preclude the advantages of relative simplicity, associated with civil MCFC systems, being gained in the use of MCFC as an AIP submarine power plant.

General Observation

The remarks regarding the protracted and slow warm through requirements on start-up of the above high temperature fuel cells, should be considered with a degree of caution; this is probably no more problematical than is charging-up batteries from cold and it is worth considering that such high temperature fuel cells are, once hot, highly responsive to load variations.

(Continued - Nero)


AIP – Fuel Cell or IHD – AIP


Integrated Hydraulic Diesel - Air Independent Power (IHD-AIP) Plant

Consistent with contemporary recycle diesel AIP systems, IHD-AIP systems are highly flexible with regards the ability to function in both diesel/LOX/argon and diesel/air regimes, offering the practical advantage of switching oxidant types, as operational circumstances allow; e.g. snorkeling or submerged operation.

The advent of compact and lightweight IHD-AIP systems, with their reduced rates of consumption of both fuel and oxidant, provides potentials for unprecedented levels of improvement, from the viewpoint of both design and operational aspects.

In the former case, as a result of the compactness of the engine component of an IHD-AIP system and reduced consumables requirement; there is considerable scope to either use a smaller vessel for a given duty or notably increase the operational envelope of an existing hull size, taking advantage of the greater economy of the IHD-AIP system.

In a comparison with a contemporary diesel power plant of equivalent power, it should be recognized, that with a reduction in oxidant requirement to approximately 1/3rd that of the contemporary system; when snorting, there is significant scope to reduce the size of the snorkel and thus its RCS and visible profile, without compromising the efficiency of the snorkeling exercise. Likewise, the overboard discharge of the products of combustion are similarly reduced, as is any thermal, chemical or acoustic signature related to same.

Unlike contemporary diesel systems and existing or proposed alternative AIP systems, an IHD-AIP system offers a high level of power plant redundancy, without resorting to using additional or auxiliary powering systems. Effectively, an IHD-AIP system provides a ready path to the development of a fully functional single power plant AIP submarine.

Typical of the compromises associated with non-IHD-AIP systems are those AIP systems that combine both fuel cell and diesel-electric/battery prime movers; each sub-system is individually able to supply a limited portion of the submarines submerged power requirement, for a predetermined period of time. In the case of the battery component remaining as the viable source of power, the submarine will revert to operation as a classic diesel-electric/battery submarine and may operate solely on battery power until the reserve charge level dictates snorkeling and battery recharging regimes. In the case of the AIP system remaining as the viable powering source, the submarine will be free to operate as an AIP powered vessel, at the much reduced powering levels associated with the type, without the ability to utilize the reserve battery power for higher speed submerged operation, once this reserve is run down. Again this will be a limited mode of operation, dictated by the on-board reserve level of fuel and oxidant required for the fuel cell power plant.

Unique amongst AIP systems, the IHD-AIP plant provides its own redundancy. With their variable geometry engine configurations, they will habitually operate on a reduced number of on-line cylinders during normal cruising and transit modes, with the balance of the engine components cylinder groups engaging/disengaging on a needs be basis, for periods of elevated power demand, such as flanking speeds. In this regard and using an engine component consisting of four cylinder groups, with a combined continuous power of 6 MW and where engine malfunction is limited to one cylinder group of the power plant, this cylinder group can be locked out and in this condition, this single power plant submarine will still be a fully functional AIP submarine, with the ability to operate at up to 4.5 MW, continuous power. More-over, even with the balance of the engine on-line and operating at maximum available power, it is quite practical to return the power plant to full functionality and power, by the simple expedient of refurbishment, employing a cylinder change-out regime. Given this expedient, it is unlikely the prime mover will be required to operate at reduced powering levels for more than a few hours.

It needs to be recognized, the above is not an unusual circumstance, as engine component refurbishment by cylinder change-out, will be the usual method of maintenance for the engine component of IHD systems, whether these are the prime movers of AIP systems or in alternative applications.

It will be an unusual circumstance that will see an IHD-AIP submarine needing to operate on all cylinders, with an actual requirement to perform a maintenance sequence; however, the ability to do so, clearly demonstrates the potential sophistication and flexibility of the IHD-AIP system. No other single power plant submarine system provides its own systemic redundancy, nor offers an equivalent level of flexibility and on-board maintainability. These simple hydraulic power plants, are free of the usual technical matters, that so limit the powering levels of the contemporary AIP powering systems, such as fuel cells. As such, IHD-AIP systems do not fall into the category of the exotic and unlike contemporary alternatives, do not suffer a variety of serious limitations on their viability. Contemporary AIP systems are expensive, far from compact and as yet, unsuited to operational use as single power plant systems and do not offer any level of systemic redundancy.

IHD-AIP systems, are the only AIP system currently promoted as single power plant systems for non-nuclear submarine applications.

Effectively, the IHD engine component of an IHD-AIP system will directly integrate into an existing recycle diesel system, replacing the contemporary diesel engine. In such a retro-fit situation, given the wish to utilize the balance of the existing system, it is realistic to point out: that the existing system would support the installation of an IHD-AIP engine component, of approximately three times the power of the original diesel engine. This is a direct result of the three-fold improvement in consumption of fuel and oxidant, which equates to roughly a three fold increase in available power for an equivalent rate of consumption of fuel and oxidant. It also follows, that operation of the retro-fitted submarine at its original submerged speeds, will allow a roughly three-fold increase in time submerged; excluding considerations associated with crew requirements. This likewise has the advantage of allowing a significant reduction in snorkeling requirements during protracted patrols, notably improving the indiscretion ratio.

As these power plants are highly suited to fully automated operational regimes, with essentially an un-manned machinery space, there is an opportunity for a reduction in crewing levels and an associated reduction in crew related requirements, including both in-hull space and consumables.

There is likewise considerable potential for refinement of these power plants and associated systems and as a result, overall vessel efficiencies can likewise be further improved. With regards further development, it may well prove practical to develop an IHD-AIP (recycle diesel) submarine, that effectively eliminates the requirement for snorkeling entirely, yet offers an endurance adequate for notably better than a 60 day patrol. This would see the advent of a non-nuclear powered AIP submarine, with true under ice and open ocean capabilities.

Nero - The above was written perhaps 15 years ago and is no less relevant today
I am not up with this new type, intergrated hydraulic diesel, , how does it work. I prosume it is more than a diesel powering a hydraulic pump. Google was of no help here.