No abstract

Gas compressor stations represent a huge potential for exhaust heat recovery. Typical installations consist of open cycle configurations with multiple gas turbine units, usually operated under part-load conditions during the year with limited conversion efficiency. At least, one of the installed unit serves as back-up to ensure the necessary reserve power and the safe operation of the station. Organic Rankine Cycle (ORC) has been proven as an economical and environmentally friendly solution to recover waste heat from gas turbines, improving the overall energy system performance and reducing the CO2 emissions. In this context, taking as reference typical gas compressor stations located in North America, the paper investigates the potential benefit of ORC application, as bottomer section of gas turbines, in natural gas compression facilities. Thus, ORC converts gas turbines wasted heat into useful additional power that can be used inside the compression facility reducing the amount of consumed natural gas and, consequently, the environmental emissions, or directed to the grid, thus furthermore earning economic benefits. Different case studies are examined with reference to two typical compressor station size ranges: a “small-medium” and a “medium-high” size range. Two different gas turbine models are considered according to most common manufacturers. Typical gas compressor stations and integrated cycle configurations are identified. Based on Turboden experience in development and production of ORCs, specific design options and constraints, layout arrangements and operating parameters are examined and compared in this study, such as the use of an intermediate heat transfer fluid, the type of organic fluid, the influence of superheating degree and condensation temperature values. Emphasis is given on thermodynamic performance of the integrated system by evaluating thermal energy and mechanical power recovery. Several key performance indexes are defined such as, the ORC power and efficiency, the specific power recovery per unit of compression power, the integrated system net overall power output and efficiency, the ORC expander and heat exchangers size parameters, the carbon emission savings, etc. The performed comparison of various configurations shows that: (i) the energy recovery with ORC can be remarkable, adding up to more than 35% of additional shaft power to the compression station in the best configuration; (ii) the ORC condensation temperature value has a significant impact on the ORC bottomer cycle and on the integrated system performance; (iii) in case of Cyclopentane, keeping the same ORC cycle operating parameters, the max specific power recovery is achieved in the direct configuration case, (iv) the bottomer cycle size can be reduced with the use of a refrigerant fluid (R1233zd(E)), compared to hydrocarbon fluids; (v) the max environmental benefit can be up to 120 kg CO2/h saved per MW of installed compression power.

Pumped hydro storage (PHS) is a crucial technology for balancing large steam power plants, and may become increasingly important for storing renewable energies. Hence, capacity ranges of PHS, as well as its dynamic response to renewable power variability, will become progressively relevant. In this paper, we focus on determining capacity ranges and efficiencies of PHS plants using conventional constant speed Francis runners, adopting unconventional runner sets, arranged in innovative fashion. In the pumping mode, it is assumed that the impellers run at a single speed, but that they can have, depending on the plant, either the same or different design capacities. In the turbine mode, it is assumed that the runners can access the well-established range from 60 to 100% of design capacity via wicket gate adjustment. In order to extend the capacity ranges with constant speed runners, bypass loops to balance the plant are considered. Because bypass operation implies losses, the possible efficiencies are studied. The results show that a) bypass is an effective means of extending capacity ranges, but high bypass ratios decrease efficiencies. b) One of the impeller sets postulated in this work offers the possibility of almost continuous capacity at high efficiencies, with relatively small capacity variation within the set.

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A comprehensive and systematic evaluation of the bottoming Organic Rankine Cycle based energy recovery system, considering a wide spectrum of gas turbines with power ratings commonly used in the offshore applications, has been conducted in this paper to demonstrate the potential benefits of this technology. In this study, emphasis is given on the thermodynamic performance of the energy system by evaluating incremental electric power recovery, thermal energy recovery and carbon emissions savings. Effects of an intermediate heat transfer fluid and the utilization of a recuperator for waste energy recovery in the Organic Rankine Cycle on the key performance indicators of the energy system are evaluated. In addition to discussing advantages and limitations of the considered configurations of the bottoming Organic Rankine cycle, it is shown that by using the proposed configurations, a significant amount of additional electric power can be produced which could be used to prevent part-load operations of gas turbines resulting in fuel savings, increased gas turbine’s components life, reduced maintenance cost, and reduced CO2 emissions — a win-win proposition for the offshore projects.