Humid Air Turbine Research Articles

Humidified micro gas turbines for domestic users: An economic and primary energy savings analysis

Micro Gas Turbines (mGTs) offer valuable advantages for small-scale Combined Heat and Power (CHP) production compared to reciprocating Internal Combustion Engines (ICEs): lower maintenance costs per kWhe, cleaner exhaust, lower vibration levels and concentration of the residual heat in a single source (the exhaust gases). Nevertheless, mGTs have lower electrical efficiencies, fact that has prevented them from penetrating in the CHP market. Hot liquid water injection—by means of a saturation tower within the micro Humid Air Turbine (mHAT) cycle—allows both improving the flexibility of heat production and the electrical efficiency of mGTs; two qualities that if enhanced would increase the economic feasibility of the technology. Although the advantages of mHAT technology have been proven from a thermodynamic point of view, its economic performance has not yet been fully investigated. This paper presents a comparison of the economic profitability and the primary energy savings of an mGT, an ICE and an mHAT unit operating in real network conditions. Our aim is to investigate whether the increase in flexibility and electrical efficiency, achieved when transforming an mGT into an mHAT, allows this technology to economically outperform ICEs. Results show that the three units are viable in scenarios with high electricity and low natural gas prices. For the cases in which investment is feasible, the revenues with mHAT are the highest: thanks to their flexibility in heat generation, mHAT units are able to run all year long. On the other hand, the greatest primary energy savings are achieved with ICE units—which have the highest overall efficiencies—while mHAT savings are substantially lower.

Evaluation of the effectiveness-NTU method for countercurrent humidifier

An analytical method is advantageous in designing and optimizing the humidifier of the humid air turbine cycle. In this paper, the energy effectiveness-NTU model for the countercurrent humidifier is built and verified by the 141 groups of test data obtained from an experimental facility of pressurized packing humidifier. The effect of pressure and inlet conditions including water/air mass flow rate ratio, inlet water temperature and inlet air wet bulb temperature on the heat capacity rate ratio and the energy effectiveness is analyzed. A sensitivity analysis is performed in order to indicate the key inlet parameter to improve the energy effectiveness of countercurrent humidifier. It is shown that the maximum deviation of the energy effectiveness calculated by the analytical method is 22.7% comparing to the experimental data. However, the maximum deviation is not more than 16% when considering the actual operating conditions for the humidifier of heat capacity rate ratio being greater than1.5. Heat capacity rate ratio changes monotonically with pressure and inlet parameters, and the energy effectiveness has an inflection point of minimum value when heat capacity rate ratio is equal to 1. Sensitivity analysis shows that water/air mass flow rate ratio is the most critical factor.

A comparative simulation study of power generation plants involving chemical looping combustion systems

This work presents a simulation study on both energy and economics of power generation plants with inherent CO2 capture based on chemical looping combustion technologies. Combustion systems considered include a conventional chemical looping system and two extended three-reactor alternatives (exCLC and CLC3) for simultaneous hydrogen production. The power generation cycles include a combined cycle with steam injected gas turbines, a humid air turbine cycle and a simple steam cycle. Two oxygen carriers are considered in our study, iron and nickel. We further analyze the effect of the pressure reaction and the turbine inlet temperature on the plant efficiency. Results show that plant efficiencies as high as 54% are achieved by the chemical looping based systems with competitive costs. That value is well above the efficiency of 46% obtained by a conventional natural gas combined cycle system under the same conditions and simulation assumptions.

Performance assessment and optimization of a combined heat and power system based on compressed air energy storage system and humid air turbine cycle

Renewable energy based power sources have grown rapidly in the past few years owing to the dual constraint of climate change and pollution control. Compressed air energy storage (CAES), as a large-scale energy storage system (ESS) technology, has huge potential to manage the intermittent renewable energy based power sources effectively. However, the compression heat generated during charge and waste heat carried in turbine exhaust during discharge are not fully recuperated in current stage. A combined heat and power (CHP) system consisting of a CAES system and a humid air turbine (HAT) system is proposed to utilize the both types of heat energy. The proposed system can boost the power output, enhance performance and improve efficiency through a simultaneous supply of power and heat. The thermodynamic analysis shows that the expansion train power can be improved about 26% compared with the conventional CAES system. The parametric analysis reveals that the exergy efficiency increases with the turbine inlet temperature (TIT) of high pressure turbine (HPT) and inlet pressure of low pressure turbine (LPT), but decreases with the TIT of LPT, L/G ratio and dry air inlet temperature of saturator. Meanwhile, the system optimization is carried out via particle swarm optimization (PSO) to determine the maximum power and exergy efficiency conditions.

A Humid Air Turbine–Organic Rankine Cycle combined cycle for distributed microgeneration

This paper analyses the integration of Humid Air microturbine and an Organic Rankine Cycle in a combined cycle for distributed generation. This integration concept maximizes heat recovery at the exhaust of the micro gas turbine combining the capacities for medium temperature heat recovery of the Organic Rankine Cycle and low temperature heat recovery of the Humid Air Turbine.The integration analysis based on different sets of organic fluids and different recovery temperatures showed that the optimal combination was achieved using toluene and R245fa for medium and low temperature Organic Rankine Cycles respectively. Their combination with the low temperature heat recovery at the Humid Air Turbine saturator maximizes the heat recovery profile from the exhaust gases.The calculations carried out reveal a 25% improvement in net power output of the dual cycle compared to the standalone Humid Air microturbine. Such improvement also affects to global efficiency, increasing it up to 52% in the optimal configuration, above the 41% estimated for the standalone Humid Air Turbine and the 33% rated efficiency of the state of art microturbine Capstone C200. The economic analysis shows that these increases in efficiency and power values make the proposed concept highly competitive, with a 15% reduction in the Levelized Cost of Electricity compared with the standalone Humid Air Turbine and a reduction of 30% compared with the micro gas turbine base case.The presented results show this novel integration as a very promising solution for distributed generation applications at power range under 200kW, due to its relative simplicity and cost.

Hydrodynamic and heat and mass transfer performances of novel ceramic foam packing to humidification tower

The humidification tower is the key unit of a humid air turbine cycle. The compactness problem of a humidification tower is crucial to the flexibility and safe operation of the cycles. This research focuses on the potential application of the novel ceramic foam corrugated packing in humidification. The hydrodynamics and heat and mass transfer performances of this packing (type FSC-1) are investigated and compared with those of the traditional structured packing (type TJH-250). The experimental results show that the specific surface area obviously increases with a competitive voidage of 93% for ceramic foam corrugated packing. In comparison with THJ-250, FSC-1 exhibits about 60% pressure drop per mass transfer unit, 50% flooding gas velocity, and no more than 37% height of gas-phase mass transfer unit. Although the ceramic foam packing has relatively low air flux, it is also promising for the compact humidification tower due to its excellent heat and mass transfer performance and low pressure loss.

T100 mGT converted into mHAT for domestic applications: Economic analysis based on hourly demand

Micro Gas Turbines (mGTs) appear as a promising technology for small-scale (up to 500kW) Combined Heat and Power (CHP) production. However, their rather low electrical efficiency limits their profitability when the heat demand is low. Hot liquid water injection in mGTs—by means of a saturation tower within the micro Humid Air Turbine (mHAT) cycle—allows both improving the flexibility of heat production and the electrical efficiency of mGTs; two qualities that if enhanced would result in an increased economic feasibility of the technology.Based on simulations performed on a Turbec T100 mGT converted into an mHAT, this paper presents an assessment of the economic profitability of both an mGT (working as a CHP) and an mHAT unit operated in real network conditions. To that end, we have used net present value, internal rate of return and discounted cash flow stream methodologies. The input to the study consists of (1) hourly heat and electricity demand profiles of two distinctive users, one located in Brussels the other in San Francisco and (2) 25 electricity and natural gas price scenarios. Our aim is to investigate whether the increase in flexibility and electrical efficiency achieved when transforming an mGT into an mHAT offsets the additional costs.Results show that in scenarios with high electricity and low natural gas prices—the relationship between these two variables depending on the user, CHP and mHAT units are economically competitive. For all the price combinations where investing in mGT technology is feasible, it is worth transforming the unit into an mHAT. Moreover, the lower the electricity demand with respect to the nominal T100 production (100kWe), the more sensitive the user is to the price at which electricity is sold to the grid and therefore, the more the feasibility of mGT and mHAT technologies depends on subsidies or primes on surplus-electricity production.

Analysis of Maisotsenko open gas turbine bottoming cycle

Maisotsenko gas turbine cycle (MGTC) is a recently proposed humid air turbine cycle. An air saturator is employed for air heating and humidification purposes in MGTC. In this paper, MGTC is integrated as the bottoming cycle to a topping simple gas turbine as Maisotsenko bottoming cycle (MBC). A thermodynamic optimization is performed to illustrate the advantages and disadvantages of MBC as compared with air bottoming cycle (ABC). Furthermore, detailed sensitivity analysis is reported to present the effect of different operating parameters on the proposed configurations' performance. Efficiency enhancement of 3.7% is reported which results in more than 2600 tonne of natural gas fuel savings per year.

ICOPE-15-1020 Hampson type heat-exchanger technology and economic evaluation for LNG re-gasification and power generation At LNG receiving terminals

The system for high utilization of LNG cold energy is proposed by use of process simulator. The proposed design is a closed loop system, and composed by a Hampson type heat exchanger, turbines, pumps and advanced humid air turbine (AHAT) or Gas turbine combined cycle (GTCC). Its heat sources are Boil-off gas and cooling water for AHAT or GTCC. The higher cold exergy recovery to power can be about 38 to 56% as compared to the existing cold power generation of about 20% with a Rankine cycle of a single component. The advantage of the proposed system is to reduce the number of heat exchangers. Furthermore, the environmental impact is minimized because the proposed design is a closed loop system. A life cycle comparative cost is calculated to demonstrate feasibility of the proposed design. The development of the Hampson type exchangers is expected to meet the key functional requirements and will result in much higher LNG cold exergy recovery and the overall system performance i.e. re-gasification. Additionally, the proposed design is expected to provide flexibility to meet different gas pressure suited for the deregulation of energy system in Japan and higher reliability for an integrated boil-off gas system.

Micro gas turbine configurations with carbon capture – Performance assessment using a validated thermodynamic model

The expected increase in distributed power generation, especially in Europe, and the necessity for a reduction in greenhouse gas emissions requires an evaluation of carbon capture application at small-scale combined heat and power plants. In this regard, a micro gas turbine (MGT), a Turbec T100, has been selected for further investigation as a baseline. A thermodynamic model validated against data obtained from a test rig has been extended to enable modeling of a CO2 capture unit. In addition, two innovative cycles, an exhaust gas recirculation (EGR) cycle and a humid air turbine (HAT) cycle, have been investigated using the selected micro gas turbine model with a focus on improved carbon capture efficiency. The thermodynamic performance indicators of all cycles, namely, the baseline MGT cycle, the EGR cycle, and the HAT cycle, all with capture unit, are presented. The results show a considerable improvement in cycle efficiency for the HAT cycle (25.8%), compared to the baseline MGT (23.0%) and EGR (22.5%) cycles. However, the surge margin is reduced markedly for the HAT cycle. It is shown that the effect of EGR on the operation of the micro gas turbine is marginal. The effects of varying ambient air temperature on the performance of all cycles as well as the effect of different recirculation percentages on the performance of the EGR cycle have also been investigated. The results confirm that the performance in the EGR cycle is less sensitive to the change in ambient temperature, compared to the other cycles. The marginal effect of various recirculation percentages on the performance of the EGR cycle is also shown in this paper.

New concept of spray saturation tower for micro Humid Air Turbine applications

The micro Humid Air Turbine (mHAT) has proven to have the highest potential of all mixed air/water micro Gas Turbines (mGTs). Turning a mGT into a mHAT however requires the installation of a saturation tower. Most common saturation towers use packing material to increase the contact area between compressed air and water. The packing material however causes a pressure drop, which has a severe negative effect on the mGT performance. To limit this pressure drop, we have developed a spray tower without packing that uses nozzles to inject water in the compressed air. In this paper, we propose a design for the spray tower based on 2-phase flow simulations. The two major constraints during the design were minimal pressure loss and tower size. A sensitivity analysis was performed in order to indicate the key parameters to obtain fully saturated air from the tower. Results of simulations showed that using a spray tower reduces the pressure losses when compared to a classic saturation tower. Sensitivity analysis showed that droplet diameter and injected water mass flow rate have the largest effect on the final size of the spray tower. Finally, a cross-current spray tower design was proposed for a Turbec T100mGT because the sensitivity analysis showed that cross-current droplets injection meets the design constraints best.

Techno-economic analysis of chemical looping combustion with humid air turbine power cycle

Power generation from fossil fuel-fired power plant is the largest single source of CO2 emission. CO2 emission contributes to climate change. On the other hand, renewable energy is hindered by complex constraints in dealing with large scale application and high price. Power generation from fossil fuels with CO2 capture is therefore necessary to meet the increasing energy demand, and reduce the emission of CO2. This paper presents a process simulation and economic analysis of the chemical looping combustion (CLC) integrated with humid air turbine (HAT) cycle for natural gas-fired power plant with CO2 capture. The study shows that the CLC–HAT including CO2 capture has a thermal efficiency of 57% at oxidizing temperature of 1200°C and reducer inlet temperature of 530°C. The economic evaluation shows that the 50MWth plant with a projected lifetime of 30years will have a payback period of 7years and 6years for conventional HAT and CLC–HAT cycles respectively. The analysis indicates that CLC–HAT process has a high potential to be commercialised.

Experimental Characterization of a T100 Micro Gas Turbine Converted to Full Humid Air Operation

Micro Gas Turbines (mGTs) were considered very promising for small-scale Combined Heat and Power (CHP) production. They however never fully penetrated the CHP market, resulting in a limited market share. Due to their low electric efficiency (30% versus 80% CHP efficiency), the operation of the mGT is strongly heat-driven. In applications with a non-continuous yearly heat demand, like domestic heating systems, the mGT would be shut down for long periods, resulting in a reduced amount of yearly running hours. These limited running hours make the mGT as small-scale CHP less profitable compared to other technologies, like reciprocating engines. Converting the mGT into a micro Humid Air Turbine (mHAT) offers a solution. The waste heat in the exhausted gases is recovered in the mHAT by evaporating auto-raised hot water behind the mGT compressor, resulting in a higher electric efficiency and a more flexible mGT operation. In this paper, we present the results of experiments on a modified Turbec T100 mGT. As a proof of concept, the mGT has been equipped with a spray saturation tower to humidify the compressed air. The goal of these experiments was to evaluate the beneficial effect of compressed air humidification on the mGT performance. Two stable runs at constant pressure ratio and rotation speed were recorded during water injection. Final electric efficiency results show a relative electric efficiency increase of 1.2% and 2.4%. These changes are however in the range of the accuracy of the measurements. Further experiments are therefore necessary to fully characterise the behaviour of the mHAT at part and nominal load. Fine-tuning of the water injection control strategy is also identified as a key parameter to reduce the auxiliary power losses.

Economic Analysis of a Micro Humid Air Turbine for Domestic Applications

Micro Gas Turbines (mGT) appear as a promising technology for small-scale (up to 500kW) Combined Heat and Power (CHP) production. However, their rather low electric efficiency limits their profitability when the heat demand decreases. Hot liquid water injection in mGTs –particularly within the micro Humid Air Turbine (mHAT) cycle– allows increasing electric efficiency by making use of the flue gas residual heat in moments of low heat demand.Based on simulations performed on a Turbec T100 mGT –modified to operate as an mHAT– installed at the VUB, this paper presents an analysis of the economic profitability of such facility running on real network conditions. The study is performed assuming typical electricity and heat demand profiles for a domestic consumer. 25 natural gas and electricity price combinations have been taken into consideration, along with two types of domestic customers –with higher and lower heat demands. Results show that the profitability of the mHAT with respect to the equivalent CHP facility increases with higher electricity and lower natural gas prices. In particular, given a certain number of CHP running hours and a natural gas price, there is a threshold for the electricity price above which the net income of the mHAT unit is always higher than that of the corresponding CHP unit. In addition, water-cleaning costs for the mHAT case appear to constitute only 1 to 2.5% of total running costs.

Experimental investigation of pressurized packing saturator for humid air turbine cycle

Humid air turbine (HAT) cycle is an advanced power generation system, and its efficiency and output power are improved by humidifying the compressed air. This humidification process is completed in the saturator. Therefore, the humidifying performance of saturator has great influence on the performance of HAT cycle. In this work, a new type packing saturator was designed and a series of experiments were carried out to study its humidifying performance. In order to improve the uniformity of the saturator inlet, a twin-tangential annular flow gas distributor was designed. Then it was authorized by China invention patents (ZL201010200778.9). Now, the mal-distribution factor of inlet air is mainly between 0.15 and 0.35 in all experimental conditions. Some key parameters of air and water at the inlet and outlet of saturator were measured at different experimental conditions. These results show the outlet humid air temperature is an important parameter for determining the humidifying amount of the saturator. The humidifying performance of the saturator is mainly affected by the inlet water temperature and the liquid/gas (L/G) ratio. At the same operating pressure, the humidity ratio of outlet humid air increases with inlet water temperature and L/G ratio. At higher inlet water temperature, the L/G ratio has a greater effect on the humidity ratio of outlet humid air. The outlet water temperature is mainly affected by the inlet gas temperature. With the increasing of inlet air temperature, the outlet water temperature increases, and it is close to the wet-bulb temperature of inlet air.

Progress of the 40 MW-Class Advanced Humid Air Turbine Tests

A 40 MW-class test facility has been constructed to verify practicability of applying the advanced humid air turbine (AHAT) system to a heavy-duty gas turbine. Verification tests have been carried out from January 2012, and interaction effects between the key components were established. First, water atomization cooling (WAC) was confirmed to contribute to both increased mass flow rate and pressure ratio for the axial-flow compressor. The good agreement between measured and calculated temperatures at the compressor discharge was also confirmed. These results demonstrated the accuracy of the developed prediction model for the WAC. Second, a control method that realized both flame stability and low nitrogen oxides (NOx) emissions was verified. Although the power output and air humidity were lower than the rated values, NOx concentration was about 10 ppm. Finally, a hybrid nozzle cooling system, which utilized both compressor discharged air and humid air, was developed and tested. The metal surface temperatures of the first stage nozzles were measured, and they were kept under the permissible metal temperature. The measured temperatures on the metal surface reasonably corresponded with calculation results.

New calculation method for thermodynamic properties of humid air in humid air turbine cycle – The general model and solutions for saturated humid air

The article proposes a new calculation method for thermodynamic properties (i.e. specific enthalpy, specific entropy and specific volume) of humid air in humid air turbine cycle. The research pressure range is from 0.1 MPa to 5 MPa. The fundamental behaviors of dry air and water vapor in saturated humid air are explored in depth. The new model proposes and verifies the relationship between total gas mixture pressure and gas component pressures. This provides a good explanation of the fundamental behaviors of gas components in gas mixture from a new perspective. Another discovery is that the water vapor component pressure of saturated humid air equals PS, always smaller than its partial pressure (f·PS) which was believed in the past researches. In the new model, “Local Gas Constant” describes the interaction between similar molecules. “Improvement Factor” is proposed for the first time by this article, and it quantitatively describes the magnitude of interaction between dissimilar molecules. They are combined to fully describe the real thermodynamic properties of humid air. The average error of Revised Dalton's Method is within 0.1% compared to experimentally-based data.

Revised Dalton's method for calculation of thermodynamic properties of unsaturated humid air and gas mixture after combustion in humid air turbine cycle

The article applies Revised Dalton's method for calculation of thermodynamic properties (i.e. specific enthalpy, specific entropy and specific volume) of unsaturated humid air and gas mixture after combustion in humid air turbine cycle. The research temperature range is from 280 K to 1600 K and pressure range from 0.1 MPa to 5 MPa. “Improvement Factor” and “Cutting Off Temperature” for unsaturated humid air are explored in depth. Two “Improvement Factor” formulas are proposed. The discovery of the changing trends of “Improvement Factors” reveals the fundamental behaviors of dry air and water vapor in unsaturated humid air. Another discovery is “Cutting Off Temperature”. It is a crucial temperature point, above which the interaction of dissimilar molecules may be omitted. Revised Dalton's method may also be applied to gas mixture after combustion. The thermodynamic properties of unsaturated humid air and gas mixture after combustion are calculated by the Revised Dalton's method. The average error of Revised Dalton's method is within 0.1% compared to experimental data.

C204 高湿分空気利用ガスタービンシステムの40MW級総合試験(OS7 高温・高効率発電)

A 40MW-class AHAT (Advanced Humid Air Turbine) test facility was built and rated output was achieved Through operations at this facility, it has been verified for the first time that the key components of the medium-class gas turbines, such as an axial compressor and multi-can combustor, can be applied to the AHAT system. The cold start-up time from ignition to rated power was about 60 minutes, which is approximately one-third that of a gas turbine combined cycle plant. NO_x concent ration was 24ppm (at 16% O2) when the humidity of combustion air was approximately a half of the commercial AHAT plant, and an outlook of achieving NO_x concentration of less than l0ppm was achieved for the commercial plant. Through continued operations at this facility, further tests to confirm operating characteristics under various conditions and component reliability will be conducted to assess system characteristics of commercial AHAT equipment.

Dynamic Simulations of the Humidification Tower for An Advanced Humid Air Turbine System

The gas turbine system known as AHAT (Advanced Humid Air Turbine) has been drawing attention. This system employs a humidification tower to increase the air mass flow at the compressor outlet. To estimate the humidifying transients, a dynamic model of the humidification tower was developed. This paper describes the humidification tower dynamics based on simultaneous differential equations considering heat and mass equilibrium of humid air, feed water, vessel materials, and packing materials. Values calculated using the model were compared to the experimental values obtained from laboratory-scale experiments. The calculation error margin was 3.8 degrees for air outlet temperature and 10.9% for air outlet absolute humidity. The developed model was then applied to a demonstration-scale conditions. The maximum change rate of absolute humidity at the humidification tower exit for startup and shutdown operations was 8.6%/s for 30 seconds. The maximum change rate of absolute humidity was influenced by the minimum area flow rate which corresponded to performance of packing materials.