Per-Åke Franck

Heat pumps in industrial processes—An optimization methodology

The optimal integration of heat pumps in industrial processes has not yet been fully understood. In this paper an optimization methodology and a method which uses the composite curves as a guideline to the correct choice of heat pump type are outlined. The selection is done by matching the shape of the composite curves against the specific characteristics of several heat pump types. Furthermore, a methodology for the optimization of the most important parameters in a heat pump system is presented. In the optimization methodology the annual cost is minimized by varying heat source and heat sink temperatures, the heat pump size and the stream or streams to be utilized as heat source and heat sink. To reveal the potential for electrically driven compression heat pumps two different examples were studied with the methodology. The first example had close composite curves and was thought to be a poor heat pump candidate. The second one had open composite curves and was thought to be a promising example. The results showed that for both examples, heat pump installations were advantageous under good economic conditions for the heat pump, i.e. low electricity price, high fuel price and low investment costs. Also reasonable payback periods were achieved. With more unfavourable conditions the payback period increased, and in extreme cases a heat pump was no longer a better alternative than pure heat exchange. This decline in potential for heat pumping was much less in the example with open composite curves than in the example with closed ones. However, the conclusion to be drawn is that there exists today a potential for heat pumps in industrial processes.

Integration of Fischer-Tropsch fuel production with a complex oil refinery

The oil refining industry is facing harder regulations on renewable content in its products. One way to meet this is to produce diesel and gasoline from gasification of biomass via a Fischer-Tropsch synthesis. In this paper, integrating a biomass-to-FT syncrude process with a refinery is compared to a stand-alone biomass-to-FT syncrude process, in terms of the consequences for CO2 emissions and energy balances. The upgrading of the FT syncrude is in both cases accomplished at the refinery, in the existing units or in new units. The studied system includes a circulating fluidized-bed biomass gasifier with a biomass input of 500 MW (50% moisture content) and a complex refinery with a crude oil capacity of 11.4 Mt/y. The integrated FT-syncrude production shows, regardless of assumptions of marginal electricity generation, the largest CO2 emission reduction. Moreover, if the almost clean CO2 stream from the biomass-to-FT-syncrude production is captured, the reduction potential can be significantly increased.

Consequences of recent gas turbine developments for industrial CHP applications

Developments in gas turbine (GT) technology have been considerable during the last few years. In this paper, consequences regarding the technical performance for industrial combined heat and power applications are discussed and the most important design parameters are identified. Some GT types, which represent different stages of the developmental trend, are analysed in the simple and the combined cycle. Both the industrial and the aero-derivative GT classes are included. Conclusions are: (i) Generally, the developments have broadened the span of achievable power-to-heat ratios (α-values). Values between 0 and 1.5 are obtainable for different GT-based schemes with acceptable total efficiencies. (ii) The total efficiencies achievable depend strongly, and differently for different GT types, on the nature of the heat demands in the industrial process. (iii) When opportunities do not exist to cool the exhaust gases in an economizer, i.e. when the stack temperature is directly given by process heat demands, the total efficiency is independent of the GT class. For both classes, however, the development has led to higher total efficiencies when the process temperature demands are high. (iv) When opportunities exist to cool the exhaust gases in an economizer (which is often the case for the simple cycle and always for the combined cycle), the industrial GT developments have given improved ability to reach a high total efficiency. The new aero-derivative types, on the contrary, are worse than the conventional ones in this respect. This can also lead to worse performance in combined cycles for the new aero-derivative types. (v) When supplementary firing is applied, however, the total efficiency is high and similar for all various units and conditions. The ‘new aero-derivative’ units have, in that case, superior α-values—especially in the combined cycle.

Gas turbines in industrial CHP applications—assessment of economics

abstract-Gas turbine (GT) units (of both the industrial and the aero-derivative type) at different developmental stages are economically assessed in both simple and combined cycle. The CHP plant supplies heat (at varying levels) to an industrial plant which currently uses some existing heating device to meet this heat requirement. The following is concluded regarding the payback periods (PBPs) obtained: (i) The CHP plant efficiencies have minor impact at high electricity-to-fuel price ratios (y values). (ii) At lower T values the efficiencies, and hence the GT type selection and nature of the heat requirement, become important. New and future GTs will then offer short PBPs, compared to conventional industrial GTs. (iii) A high electrical efficiency does not regularly imply short PBPs-sometimes the situation is actually the opposite. (iv) With an advanced GT or a combined cycle the electricity production for a given heat requirement can be substantially increased, compared to that for a less advanced GT, without any substantial increase in PBP (provided that these three systems are all designed for high total efficiencies and have similar investment costs). (v) A PBP rank ordering of various CHP options is not affected by the magnitude of the ~ value. With a life-cycle cost method, CHP plants with high power-to-heat ratios (such as the most advanced simple cycle GT and combined cycles) will be put in a favourable light-particularly if the profitability requirement is low. The rank ordering of these plants also benefits from a high y value.

Process integration of various types of heat pumps

To install a heat pump correctly in an industrial process is not only a question of heat pump optimization. The way the integration is made will at least have as much influence on the final result as the efficiency of the heat pump itself. Therefore a simultaneous optimization must be made which takes both the heat pump and the process into account.