Enhancement of solar energy use by an integrated system for five useful outputs: System assessment

Rising population and industrialization made desalination of prime importance in physically water scarce Sultanate of Oman for fulfilling the gap between the rising demand and supply of fresh water. Almost 80-85% of the installed and planned desalination plants in the Sultanate are based on Combined Cycle Gas Turbine (CCGT) power plants while remaining are standalone which includes about 5-7% of the installed plants for rural arid and dry regions. All the installed and planned desalination plants utilises fossil fuels for their operation and are based on Reverse Osmosis (almost 90-95% of the plants) and Multi Stage Flash technologies. Sultanate of Oman is a tropical country with most of the regions being arid and dry receiving solar energy most abundantly. But the utilisation of solar energy in the country is mostly limited to installations based on photovoltaic systems. Only recently solar thermal Enhanced Oil Recovery plant with 1 GWth power output has been undertaken in the country at Amal oil field. A pilot standalone Multi Effect Desalination (MED) plant using fixed focus type Scheffler concentrator for remote and arid rural regions of country has been discussed in this paper to address this gap. This pilot plant has been designed for producing 100 kg/day output based on three stage cross flow type multi effect desalination technology with two 16 m2 Scheffler concentrators and operates in the temperature limits of 170 – 90°C. Preliminary testing carried out on the system during summer and winter period has shown that with available insolation above 700 W/m2, steam at a pressure of 8 to 8.5 bar could be generated in a batch experiment after 2-3 hours from starting the operation for 42 to 55 kg of water in the header of the system. This steam generated is further utilised for desalination in three stages. The initial lag period for the system is measured to be 35-50 minutes depending on the quantity of water in the header, wind speed and solar insolation. System comes out of the lag period when solar insolation reaches just above 650-700 W/m2. The desalination output for the system is measured between 60-65 litres per day for the summer period. Batch type intermittent operation, tracking errors, optical concentration losses, receiver convection losses, brine heat losses are few of the reasons observed based on the analysis for the lower output from the system. Experimentation has given a direction to make operation of the system from batch to continuous production while reducing optical and convection losses through appropriate rectifications for increasing overall yield of the system.

This study investigates the retrofitting of a 25 MW gas turbine (GT) power plant in River State, Nigeria, into a combined cycle gas turbine (CCGT) system for the enhancement of energy efficiency and performance through exhaust heat recovery. Performance data over 37 days was analyzed using SCILAB software, concentrating on maximization of net power output and energy efficiency; and minimization of specific fuel consumption and pollutant emissions. The best performance of the GT power plant indicated a net power output of 21.99 MW, thermal efficiency of 28.89%, and a specific fuel consumption (sfc) of 0.26 kg/kWh on the day 31. In the optimization process, the retrofitted combined cycle gas turbine system showcased a design net power output of 50 MW (25 MW from both gas turbine and steam turbines) and a thermal efficiency of 61.35%. Between 36.63 and 50.53 MWth of waste heat is harnessed during the retrofitting process, thereby contributing to significant minimization of fuel consumption as well as pollutant emissions. This indicates the potential of converting gas turbine power plants into combined cycle gas turbines power plant for improvement in efficiency and sustainability in electricity power generation. This study’s unique contributions include: (i) the integration of supplementary-fired HRSG for a 25MW gas turbine using actual plant data from Rivers state, Nigeria, (ii) the use of SCILAB for comprehensive cycle modeling and optimization, (iii) fuel-specific performance analysis using regional natural gas composition, and (iv) validation of performance enhancement under high ambient temperature conditions relevant to Sub-Saharan Africa. The findings demonstrate that retrofitting OCGT plants with HRSGs and supplementary firing can substantially improve energy efficiency and sustainability in gas turbine-dominated power sectors like Nigeria’s.

Waste heat recovery is an underutilized strategy for reducing emissions and mitigating climate change. High-temperature exhaust from gas turbines (GTs) is often not utilized, leading to both energy losses and emissions. This study proposes a novel WHR system that integrates a supercritical carbon dioxide (sCO2) Brayton cycle with a concentrated solar power (CSP) component, including thermal energy storage, for GT heat recovery. The WHR system boosts overall efficiency, sustainability, and economic performance by harnessing GT exhaust and solar-derived heat. One application of GTs is providing off-grid electricity to remote mining operations. A comprehensive techno-economic simulation model is developed, and a case study for a mining site in Western Australia is presented. The results show that the proposed CSP–sCO2 WHR system can provide an additional 56,028.78 MWh/year at a levelized cost of electricity (LCOE) of $0.0597/kWh, substantially increasing the output of the GT plant while reducing emissions and costs. Compared to a standalone CSP–Rankine plant, the proposed system halves capital expenditures, cutting LCOE by $0.0246/kWh. The proposed WHR system highlights the potential for reducing emissions and fuel costs in GTs, while the comparison with CSP–Rankine demonstrates how integrating CSP with waste heat can help achieve CSP LCOE targets.

The study provides technoeconomic evaluations of advanced MEA-based Post-Combustion CO2 Capture (PCCC) process configurations applied to a 750 MW Combined Cycle Gas Turbine (CCGT) power plant. Rigorous rate-based model of the PCCC process developed in Aspen Plus was validated and then used to study synergistic effects of combining three process configurations in one flowsheet using energy and levelized cost of capture as key performance indicators (KPIs). The results of the energy and economic analysis elucidate that Absorber Inter Cooling (AIC) + Rich Solvent Split (RSS) + Lean Vapor Compression (LVC) is the optimal combination of MEA-based PCCC process as it provided minimum regeneration energy (2.80 GJ/tCO2) and levelized capture cost (72.7 $/tCO2) representing an overall energy and cost savings of 6.25% and 8.95%, respectively. The study demonstrates that the usage of single KPI such as energy savings can provide misleading results. For example, combination of AIC + RSS + Inter Heated Stripper (IHS) provided maximum equivalent energy savings (3.50%), however, it did not result in highest cost savings due to high capital and operating costs of additional heater and pump. Overall, the study underlines the potential of advanced mature technologies on energy and cost reductions.

Simulation and optimization of a combined cycle gas turbine power plant under part-load operation

On existence of trends applicable to thermoeconomic optimisation of combined cycle gas turbine power plants

Thermoeconomic optimisation of heat recovery steam generators of combined cycle gas turbine power plants considering off-design operation

A conceptual design assessment shows that the use of structured adsorbents in a regenerative adsorption wheel is technically feasible for the application of selective exhaust gas recirculation (SEGR) in combined cycle gas turbine (CCGT) power plants. As the adsorber rotates, CO2 is selectively transferred from a flue gas stream to an ambient air stream fed to the gas turbine compressor, increasing the CO2 concentration and reducing the flow rate of the fraction of the flue gases treated in a post-combustion CO2 capture system. It imposes an estimated pressure drop of 0.25 kPa, unlike a pressure drop of 10 kPa reported for selective CO2 membrane systems, preventing a significant derating of the gas turbine. An equilibrium model of a rotary adsorber with commercially available activated carbon evaluates the inventory of the adsorbent and sizes the wheel rotor. Two rotary wheels of 24 m diameter and 2 m length are required per gas turbine—heat recovery steam generator train to achieve an overall CO2 capture level of 90% in a CCGT power plant (ca. 820 MWe) with SEGR “in parallel” to the capture plant. Two to five rotary wheels are required for a configuration with SEGR “in series” to the capture plant. A reduction of 50% in the mass of the adsorbent would be possible with Zeolite 13X instead of activated carbon, yet the hydrophilicity of zeolites are detrimental to the capacity and upstream dehydration of the flue gases is required. A parametric analysis of the equilibrium properties provides guidelines for adsorbent development. It suggests the importance of balancing the affinity for CO2 to allow the regeneration of the adsorbent with air at near ambient pressure and temperature, to minimise the inventory of the adsorbent within practical limits. An adsorbent with a saturation capacity of 8 mol/kg, a heat of adsorption from 24 to 28 kJ/mol CO2 and a pre-exponential factor of the equilibrium constant from 2 × 10–6 to 9 × 10–6 kPa−1 would result in an inventory below 200 kg, i.e., approximately the limit for the use of a single rotary wheel system.

The paper presents the research outcome on integration of an Adiabatic Compressed Air Energy Storage system with a Combined Cycle Gas Turbine power plant to increase its operation flexibility. The study demonstrates the novel hybrid CCGT-ACAES plant including an extended operational load level range and increased operation flexibility which supports the power grid to allow more power generation from connected intermittent renewable energy sources. It is also shown that this new hybrid power plant will avoid the Combined Cycle plant gas turbine operating under the low load level. Lowering the minimum hybrid plant operational load level during air and Thermal Energy Storage charging process to the required minimum Heat Recovery Steam Generator load level eliminates the need for Combined Cycle Gas Turbine plant cycling operation increasing the lifetime of the plant components. Adiabatic Compressed Air Energy Storage plant concept is based on proved and well established direct two-tank Thermal Energy Storage technology used in Concentrated Solar Power plants. Improved hybrid plant flexibility is occupied by slight decrease (2%) in the plant efficiency. Further investigation into alternative advanced Thermal Energy Storage systems based on latent heat and chemical reaction heat would offer better hybrid plant round-trip efficiency across operational plant load level range.

New operating strategy for a combined cycle gas turbine power plant

Simulating combined cycle gas turbine power plants in Aspen HYSYS

Combined cycle gas turbine (CCGT) power plants must often run at part-load conditions, as the electricity demand varies constantly. We present a method and necessary correlations for simulating the part-load operation of a typical CCGT plant in a commercial simulator (e.g. GateCycle). We show that assuming constant values for some equipment parameters (e.g. efficiencies) and ignoring the operating maps of key equipment can overestimate plant performance significantly at part-loads. Furthermore, a rise in the ambient temperature lowers the plant capacity, but increases the plant efficiency. Then, we propose a simulation-based optimization approach that yields an optimal operating strategy to maximize the overall plant efficiency for any part-load. Our strategy forms a basis for evaluating the two widely used operating policies (fuel flow control or FFC and inlet guide vane control or IGVC). Our proposed strategy increases the plant efficiency by as much as 2.63% (absolute) over FFC and 0.93% over IGVC. This work highlights the need for integrating the two cycles (gas turbine and steam) to optimize the plant performance. We find that FFC seems to prioritize the gas turbine and IGVC tends to prioritize the steam cycle, while our proposed strategy strikes an optimal balance between the two.

The impact of the new investments in combined cycle gas turbine power plants on the Italian electricity price

Simulation of a combined cycle gas turbine power plant in Aspen HYSYS

This paper presents a reliability analysis of a combined cycle gas turbine (CCGT) power plant. A Multi-state Markov model is introduced for a two-shaft CCGT where combustion turbine and steam turbine are coupled to a proper generator. The model is a suitable representation for both base load unit and intermittent operating unit. By using the model, such reliability characteristics as Forced Outage Rate, Equivalent Forced Outage Rate, etc. can be easily calculated. Sensitivity analysis for reliability data uncertainty is also provided. The numerical example based on real world combined-cycle power plant is presented in order to illustrate the model application.