Powerplant Thermodynamics and CAABUS Design Concept

Research Paper (postgraduate) , 2023 , 17 Pages

Engineering - Power Engineering

In this work, regenerative and concentrated solar power (CSP) plants are examined for potential improvement in their operating efficiencies.

The influence of the working fluid flow-rate and the vaporizer temperature on power generation was evaluated. Also, a novel waste recovery engine array model is described. In order to improve the thermal efficiency, consideration must be given to the range of values of the operating parameters, so as to attain the maximum efficiency value at the lowest possible cost.

Power production in a developing nation like Nigeria has been witnessing incessant interruption. In this work, a power plant array with scalable potential is considered, suited to low-density population centers. One of the proposed application areas is the campus of University of Nigeria, Nsukka. Besides, regenerative and concentrated solar power (CSP) plants are examined for potential improvement in their operating efficiencies.

Thermodynamic Modelling of CSP and Regenerative Plants with Engine Scalability

Nwachukwu Paul Nwachukwu*, Wilfred Ifeanyi Okonkwo** and Izuchukwu Francis Okafor **

*Technuell Services

** NCERD, University of Nigeria, Nsukka, Nigeria

In this work, regenerative and concentrated solar power (CSP) plants are examined for potential improvement in their operating efficiencies. The influence of the working fluid flow-rate and the vaporizer temperature on power generation was evaluated. Also, a novel waste recovery engine array model is described. In order to improve the thermal efficiency, consideration must be given to the range of values of the operating parameters, so as to attain the maximum efficiency value at the lowest possible cost.

Keywords: CSP, Regenerative, Rankine, Automotive; Scavenger; Thermal efficiency; Thermodynamics

Nomenclature

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1.0 Introduction

Power production in a developing nation like Nigeria has been witnessing incessant interruption. In this work, a power plant array with scalable potential is considered, suited to low-density population centers. One of the proposed application areas is the campus of University of Nigeria, Nsukka. Besides, regenerative and concentrated solar power (CSP) plants are examined for potential improvement in their operating efficiencies.

It is reported that Nigeria has poor power statistics [1]. In investigation pertaining to modelling, Ho et al [2] studied the Organic Flash Cycle (OFC) and other advanced vapor cycles for intermediate and high temperature waste heat reclamation and solar thermal energy applications, and concluded that aromatic hydrocarbons were better suited to working fluids due to their higher power output; requiring less complex turbine designs. Badr et [3] conducted a simulation study on the performance of Rankine-cycle plants, which used steam as the working fluid and developed a BASIC programme to facilitate the prediction of optimal design operating condition of the plants. Kumar and Kasana [4] conducted a study on a rankine cycle plant, and showed that the efficiency can be improved by using an intermediate reheat cycle. Chen et al [5] studied Rankine and supercritical Rankine cycles for the conversion of low-grade heat into electrical power and concluded that the thermodynamic and physical properties, stability, environmental impact, safety, compatibility, availability and cost are important considerations for selecting a working fluid. Geete and Khandwawala [6] obtained correction curves for power output with respect to a 120 MW thermal power plant. Also, Jamal [7] conducted a comparative study into the working fluids of Organic Rankine Cycles (ORC). It was determined that the temperature profile in the evaporator and condenser was connected to exergy losses and best energy utilization.

In this work, regenerative and concentrated solar power (CSP) plants are examined for potential improvement in their operating efficiencies. The influence of the flow-rate of the working fluid and the vaporizer temperature on power generation was evaluated. With this operating condition, the gains in the thermal efficiency justify operating the plant below a threshold value. Also, a novel waste recovery engine array model is described – in addition to a patented mechanism of a controlled auxilliary billed power utility system (CaaBUS).

2.0 Automotive System Potential

In Figure 1, a view of daily power availability and average allocation to (registered) customers is shown. In Figure 2, heavy-duty truck vehicles are shown. In the country, there are a number of thermal stations, one of such is the Egbin power station, Figure 3. Figure 4 shows a concept diagram of heavy-duty truck diesel engines coupled to a mechanical/hydraulic linkage. The aggregate (generated) power is that of the combined output of the engine array. In the figure, there are components which include a fuel storage tan, grid system with autonomous control. Also, there is a prospect of co-generational application.

The plant is suited to low-density population centers. One of the proposed application centers is the campus of University of Nigeria. The university has over 36000 students [1,8]. Since its inception it has potentially relied on grid power and stand-alone generators. There have been power interruptions which may have affected to some extent research, comfort of living and business within its main campus in the Nsukka metropolis. With potentially low maintenance cost and availability of service manpower, there is the prospect for adaptive improvement. Further, by coupling internal combustion engines of long-haulage vehicles of about 500KW capacity, there is the potential for specialized power production. The plant herein referred to as controlled auxilliary billed power utility system (CaaBUS), should be able to provide power for the residents of the university, potentially, as well as for academic and commercial purposes.

The patented mechanism of the CaaBUS array is developed from the system in Fig. 5. The device comprises adjustable cylindrical metal roller(s) (1), mounting wedge (2), Pulley-belt system (3), clutch system (4), generator (5), shaft (7), energy Storage (8), vehicle (9), inflatable tube (10), under-hood thermoelectric absorber and generator (13) and a pump (11). There is also an automation control panel with torque, load and temperature sensors, Fig. 5 A for the regulation of load and power output, this can communicate independently with other devices to switch power and/or off the car-ignition and throttle system to the back-up power mode in the advanced design type. The manual system (Fig. 5B) comprises the aforementioned without the panel but the clutch system is potentially useful to suspend the transmission of torque. The lithium-ion battery stores the excess energy and this can be used when the vehicle ignition is not operational, and for running the back-power mode. Figure 5C shows the inflatable tube-pump system, for lifting the vehicle off the frame arrangement with an under-hood thermoelectric absorber and generator. A vehicle idling over the members including a set of pulley mechanism is illustrated, (Figure 5D).When the car idles over the device - with or without an automatic transmission - the throttle is controlled by a mechanism that depresses the pedal to the required position; the engine speed could be matched to the load demand by a control spring-loaded device attached to the throttle. The throttle adjustable device comprises a spring-loaded screw device. The inflatable–tube is embedded at the center of the frame, compressed air is supplied from the back-up pump device and the tube is inflated as the vehicle what to disengage the system and re-inflated vice-versa. The compressed tube is used to minimize the impact of the vehicle weight on the frame arrangement and the vehicle suspension.

3.0 Cycle Description

In Figure 6, a regenerative rankine plant is shown with a related temperature-entropy (T-s) diagram, Figure 7. The components of the regenerative plant include: boiler/vaporizer, superheater, turbine, condenser, regenerator and pump.

4.0 Theory - Regenerative Rankine Plant

The thermodynamic equations are formulated from energy and mass balances

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5.0 Theory - CSP Plant

The CSP plant (Fig.8) operates on the basis of the Rankine cycle principle. The temperature entropy (T-s) diagram is shown in Fig. 9. The energy and mass balances are written as:

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6.0 Results and Discussion

6.1 Regenerative Rankine Plant

Figure 10 shows the plot of the thermal efficiency and the vaporizer temperature. The thermal efficiency increases with temperature. At vaporizer temperature values < 300C, there are deviations in the efficiency values. With this operating condition, the gains in thermal efficiency justifies operating the plant optimally, this important in the design and operation of energy-efficient power plants. It is seen that significant gains in the efficiency can be obtained at high superheat temperatures and pressures.

In Fig 11, the plot of the thermal efficiency and turbine outlet pressure is shown. The plot indicates that relatively high thermal efficiency values are obtained at high vaporizer temperatures for low values of turbine outlet pressure; giving an indication of the turbine capacity to convert heat to power. The turbine outlet temperatures are typically low [13].

In Fig. 12, it is observed that peak power production is not necessarily attained at the maximum thermal efficiency value; hence the need for the optimization of the operating fundamental variables.

6.2 CSP Plant

In order to improve the thermal efficiency of power plants, consideration must be given to the range of values of the operating parameters, so as to attain the maximum efficiency value at the lowest possible cost. The plot of power production at various vaporizer pressure is shown in Fig. 13. The power generation peaks at the maximum vaporizer pressure. Potentially, the plant can operate at peak thermal efficiency if the operating parameters were optimized. Thus, operating a thermal plant at the peak efficiency could entail considerable cost for power production.

In Figure 14, it is seen that the power generation potential of the CSP plant increases significantly with temperature, between 250C and 350C. In low to intermediate vaporizer temperatures, power generation is not significantly affected by vaporizer pressures, so for multi-turbine thermal plants as in this case, high operating temperatures will result to significant power output for a given pressure value.

In Fig.15, the influence of the flow-rate of the working fluid and the vaporizer temperature on power generation is evaluated. At high flow rate and high degree of superheat, generated power increases; and sharply within a range of vaporizer temperatures of 230C-250C; emphasizing the need to appropriately select the operating temperatures for a given flow-rate.

Conclusion

The influence of the flow-rate of the working fluid and the vaporizer temperature on power generation was evaluated. The thermal efficiency of the regenerative plant increased with temperature: at vaporizer temperature values < 300C, there were deviations in the efficiency values. With this operating condition, the gains in thermal efficiency justify operating the plant below a threshold value. For the CSP plant, power generation peaked at the maximum vaporizer pressure. Potentially, the plant can operate at peak thermal efficiency if the operating parameters were optimized. Novel engine array system coupled to a power turbine is described. With potentially low maintenance cost and availability of service manpower, there is the prospect for improvements efficiency.

Acknowledgement

The response of Dr S Udo-Etuk of the Department of Mechanical Engineering, University of Uyo is acknowledged.

Funding and/or Conflicts of interests/Competing interests.

Declaration - This manuscript has no conflict of interests/competing interests.

References

[1] Nigeria: The True Cost of Electricity –NESG,http://iwin.org.ng/index.php/2014-10-11-16-33-00/daily-hours-of-supply-availability
[2] Tony H, Samuel SM, Ralph G. Comparison of the Organic Flash Cycle (OFC) to other advanced vapor cycles for intermediate and high temperature waste heat reclamation and Solar Energy, Energy 2012, 42, 1:213–223
[3] Badr O, Probert SD, O'Callaghan PW. Selecting a working fluid for a Rankine-cycle engine Applied Energy 1985, 21 : 1–42
[4] Kumar Kapooria R.K., Kumar S and Kasana K S, An analysis of a thermal power plant working on a Rankine cycle: A theoretical investigation Journal of Energy in Southern Africa, Vol. 19 No 1, February 2008
[5] Huijuan CD, Yogi G, Stefanakos EK.A review of thermodynamic cycles and working fluids for the conversion of low-grade heat Renew Sustain Energy Rev 2010;14:3059–6
[6] Ankur G and Khandwawala A.I, Thermodynamic analysis of 120 MW thermal power plant with combined effect of constant inlet pressure (124.61 bar) and different inlet temperatures, Case Studies in Thermal Engineering , 2013; 1,1,:17–25
[7] Nouman J, Comparative studies and analyses of working fluids for Organic Rankine Cycles - ORC Master of Science Thesis, KTH School of Industrial Engineering and Management Energy Technology, Sweden, 2012
[8] About University of Nigeria Nsukka, https://www.timeshighereducation.com/world-university-rankings/university-nigeria-nsukka
[9] Geopolitical Regional Map of Nigeria, www.uspf.gov.ng,Universal Service Provisional Fund,2015
[10] Trucks articulated truck pullover by Ibadan Express Way, https://www.alamy.com/trucks-articulated-vehicle-pullover-layby-ibadan-highway-lagos-nigeria-image63677775.html
[11] Egbin Power Station Targets-2670MW of Electricity by 1. 2017,.hopefornigeriaonline.com, 08 July 2017
[12] Steam turbines for solar thermal power plants,https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.solarthermalworld.org/sites/default/files/powergeneration.pdf&ved=2ahUKEwiIsfLQ5qn1AhXmkosKHbAsBMsQFnoECAsQAQ&usg=AOvVaw1gMHyGxl12NdJ3pXRcq5VL
[13] Yunus AC and Michael AB, Thermodynamics, an Engineering Approach. 5th ed., McGraw-Hill, 2006

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Figure 1: Estimate of average hours of power supply per day/load allocation per registered customer in the geopolitical zones of Nigeria; calculated from data in [9]

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Figure 2: Trucks Articulated Vehicles at Lagos-Ibadan Highway [8]

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Figure 3: One of the Largest Thermal Power Stations in Nigeria formerly managed by the Power Holding Company Company of Nigeria [10]

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Figure 4: Conceptual diagram of the controlled auxilliary billed power utility system (CaaBUS)

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Figure 5: A, Mechanism of the CaaBUS without the auxiliary components for simple configuration with a torque meter and electric meter (14); B, Mechanism of the CaaBUS without the auxiliary components for simple configuration with a torque meter and electric meter (14); C, An Inflatable tube-pump system for lifting the vehicle off the frame arrangement with an under-hood thermoelectric absorber and generator; D, A vehicle idling over the members including a set of pulley mechanism

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Figure 6: Thermodynamic cycle of the regenerative rankine power plant

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Figure 7: Temperature-entropy (T-s) diagram of the regenerative rankine cycle

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Figure 8: Schematic and process diagram of the CSP plant [11]

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Figure 9: Temperature-entropy (T-s) diagram of the CSP plant [12]

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Figure 10: Variation of thermal efficiency of the regenerative rankine cycle with vaporizer temperature and pressure

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Figure 11: Variation of thermal efficiency with turbine outlet pressure

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Figure 12: Plot of Illustrations are not included in the reading sample and Illustrations are not included in the reading sample with varying vaporizer pressure

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Figure 14: Evolution of Illustrations are not included in the reading sample and thermal efficiency with vaporizer temperature Illustrations are not included in the reading sample

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Figure 15: Plot of Illustrations are not included in the reading sample with varying vaporizer temperature Illustrations are not included in the reading sample

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Figure 16: Evolution of Illustrations are not included in the reading sample with flow rate varying working fluid flow rate Illustrations are not included in the reading sampleand vaporizer temperature Illustrations are not included in the reading sample

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• Authors: Paul Nwachukwu (Author), Okonkwo Wilfred (Author), Okafor Izuchukwu (Author)
• Publication Year: 2023
• Pages: 17
• Catalog Number: V1442972
• ISBN (PDF): 9783963554612
• ISBN (Book): 9783963554629
• Language: English
• Tags: powerplant, thermodynamics, caabus, design, concept