Modelling and Performance Analysis of the Rolls-Royce Fuel Cell Systems Limited: 1 MW Plant

Abstract

This paper is focused on the performance of the 1MW plant designed and developed by Rolls-Royce Fuel Cell Systems Limited. The system consists of a two stage turbogenerator coupled with pressure vessels containing the fuel cell stack, internal reformer, cathode ejector, anode ejector and off gas burner. While the overall scheme is relatively simple, due to the limited number of components, the interaction between the components is complex and the system behaviour is determined by many parameters. In particular two important subsystems such as the cathode and the anode recycle loops must be carefully analyzed also considering their interaction with and influence on the turbogenerator performance. The system performance model represents the whole and each physical component is modelled in detail as a sub-system. The component models have been validated or are under verification. The model provides all the operating parameters in each characteristic point of the plant and a complete distribution of thermodynamics and chemical parameters inside the SOFC stack and reformer. In order to characterise the system behaviour, its operating envelope has been calculated taking into account the effect of ambient temperature and pressure as described in the paper. Given the complexity of the system various constraints have to be considered in order to obtain a safe operating condition not only for the system as a whole but also for each of its parts. In particular each point calculated has to comply with several constraints such as stack temperature distribution, maximum and minimum temperatures and high and low pressure spool maximum rotational speeds. The model developed and the results presented in the paper provide important information for the definition of an appropriate control strategy and a first step in the development of a robust and optimized control system.

High Efficiency SOFC Power Cycles With Indirect Natural Gas Reforming and CO2 Capture

“…By this point of view, these preliminary results evidence that the plant layout would require further evolution to get closer to an engineering feasibility. On the other hand, the analysis also confirms the better perspectives of different power plant solutions discussed in literature, which exploit internal reforming within the FC (with no separated heat transfer loops as those required by the power plant considered here) to simplify the plant heat management, both for applications without CO 2 capture [9,10] and for CCS [3,4,11,12].…”

“…Depending on the SOFC integration with the natural gas reforming/shift section, two main plant solutions can be identified: (i) systems where natural gas is-partially or totally-internally reformed in the FC [6] and (ii) systems where natural gas is reformed before the FC, which is therefore fed with a high hydrogen syngas [7,8]. Cycle configurations of the first type are the most commonly considered by developers of high efficiency power generation plants based on SOFCs and gas turbines [9][10][11]. In both cases, CO 2 can be separated downstream the FC with a "post-FC capture" layout, via a range of available technologies, e.g., chemical separation processes [3,12,13], physical separation processes [4,[14][15][16], oxy-combustion [11,[17][18][19][20][21], and cryogenic methods [22].…”

Predicting the ultimate potential of natural gas SOFC power cycles with CO 2 capture – Part A: Methodology and reference cases

“…In order to avoid excessive thermal stresses through the fuel cell, gas temperature increase along the stack should be limited. To this end, heat can be recovered from the gases leaving the fuel cell (or the combustor if adopted) by means of high temperature heat exchangers (600e800 C) [26,30,51] or by recycling and mixing part of the cathode exhaust with fresh air [52,53]. While the first option implies the use of expensive material, the second requires the adoption of an ejector to sustain the recycle, thus increasing the auxiliary electric consumptions (fresh air needs to be pressurized to serve as primary driving gas in the ejector).…”

“…It is worth nothing that in both cases steam required for NG reforming is supplied by recirculating part of the anodic product through an ejector rather than generating steam in a dedicated heat exchanger. Although this plant modification departs from the SOFC configuration described in Section 3.2, the cell anodic recycle is a well-known solution (applied in the past [14,52] as well as today by several of the quoted manufacturers) which eliminates the need of steam pipeline and heat exchanger system, taking steam from the oxidized products to sustain the reforming process. This arrangement avoids additional water consumption and the costs associated to water treatment; an issue of utmost importance for medium/large scale applications as those studied in this work.…”