A Polygeneration Process Concept for Hybrid Solar and Biomass Power Plant: Simulation, Modelling, and Optimization

Preface

The global warming phenomenon, as a significant sustainability issue, is gaining worldwide support for the development of renewable energy technologies. The term ‘polygeneration’ is referred to as an energy supply system, which delivers more than one form of energy to the final user, for example, electricity, cooling, and desalination can be delivered from the polygeneration process. The polygeneration process in a hybrid solar thermal power plant can deliver electricity with a lesser impact on the environment compared to a conventional fossil fuel based power generating system. It is the next generation energy production technique with a potential to overcome the intermittence of renewable energy.

In this study, the polygeneration process simultaneously with production of power, vapor absorption refrigeration (VAR) cooling, and multi-effect humidification and dehumidification (MEHD) desalination systems from different heat sources in hybrid solar-biomass (HSB) systems with higher energy efficiencies (energy and exergy), primary energy savings (PES) and payback period, are investigated.

There are several aspects associated with hybrid solar-biomass power generation installations, such as state wise availability of biomass resources and solar direct normal irradiance (DNI), have been analyzed. Month wise solar and biomass heat utilization has also been analyzed for hybrid systems in four regions of India (East: Guwahati, Assam; West: Udaipur, Rajasthan; North: Delhi, South: Madurai, Tamil Nadu). The month wise daily average solar radiation is considered as 20%, 40%, 60%, and 80% and remaining heat is taken from biomass resources in the northern region (Delhi) in the proposed hybrid plant.

The thermodynamic evaluation (energy and exergy) of the HSB power plant has also been investigated. The total input energy of the proposed hybrid system is taken from the heat transfer fluid through a parabolic trough collector (PTC) per availability of solar resources and from remaining biomass to maintain steam, at a superheated state of 500°C and 60 bar, and supplied to turbines at a steam mass flow rate of 5 kg/sec. The energy and exergy analyses of a 5 MW HSB system with series mode was carried out to identify the effects of various operating parameters like DNI, condenser pressure, turbine inlet temperatures, boiler pressure on net power output energy, and exergy efficiencies.

The VAR cooling system operates using the extracted heat taken from turbine and condenser heat of the VAR cooling system is used in a MEHD system for production of drinking water, per demand requirement. Though the production of electricity decreases due to extraction of heat from turbine for VAR cooling and MEHD desalination, the complete system meets the energy requirements & increases the PES.

The thermodynamic evaluation (energy and exergy), optimization and payback period of the polygeneration process in an HSB thermal power plant for combined power, cooling, and desalination is investigated to identify the effects of various operating parameters. The system has achieved a maximum energy efficiency of 49.85% and exergy efficiency of 20.94%. The primary energy savings of the polygeneration process (PESPP) in an HSB system is achieved at 50.5%. The electricity generation from the polygeneration process increased to 78.12%, as compared to a simple thermal power plant. The payback period of the polygeneration process in an HSB thermal power plant is 1.5 years, which is less than a solar thermal power plant, HSB thermal power plant, an cogeneration in an HSB thermal power plant.

The modeling, simulation, optimization, and cost analysis of polygeneration hybrid solar biomass systems has been carried out in this book. The simulation is performed in EES Software. Availability of both solar resources (DNI, ambient temperature, and wind speed) and biomass in the same regions/places is highly desirable to design and simulate for a hybrid solar thermal power plant. An introduction to this discussion begins in Chapter 1 and state of art of concentrated solar thermal technologies for end use applications are addressed in Chapter 2. Resource assessment of solar and biomass technologies for hybrid thermal power plants in India is discussed in Chapter 3. In this chapter, several aspects associated with hybrid solar and biomass power generation installations, such as state wise availability of biomass resources and DNI, have been discussed. The DNI is based on daily averaging of DNI mapping, resulting from the data available with the National Renewable Energy Laboratory (NREL) and National Institute of Solar Energy (NISE). These DNI resource analysis results are a reliable indication of solar potential. For assessing the solar energy potential, only 10% of the total waste land area available has been considered in major biomass energy contributing states like Punjab, Uttar Pradesh, Haryana, Maharashtra, Madhya Pradesh, Karnataka, Tamil Nadu, Gujarat, Rajasthan, Kerala, Bihar, Andhra Pradesh, West Bengal, Odisha, and Assam. For biomass resources, the assessment of scale up potential on biomass has been carried out separately for biomass crop residues and energy plantations. The major agricultural based biomass crop wise potential for different states of India are mapped by analyzing the energy potential of the biomass. The solar thermal power plant and case study is discussed in Chapter 4. A simulation study of biomass consumption in the power plant at different radiation conditions to meet heat requirements for the operation of solar hybrid power plants is also carried out. The modeling and simulation of hybrid solar and biomass thermal power plants is discussed in Chapter 5. For the hybrid system, a biomass boiler arrangement is taken to operate on the biomass whenever it is needed at different load conditions. A solar field is utilized to heat the heat transfer fluid per availability of DNI. Hot water from a feed water heater gets heated through heat transfer fluid using a heat exchanger. The total input energy of the proposed hybrid system is taken from the heat transfer fluid through PTC per availability of solar resource and remaining biomass to maintain the steam at a superheated state supplied to turbine. The detailed performance analysis (energy and exergy) of solar and biomass hybrid thermal power plants are carried out to identify the effects of various operating parameters like DNI, condenser pressure, turbine inlet temperatures, boiler pressure on net power output energy, and exergy efficiencies. A 5 MW hybrid solar and biomass power plant has been designed. The hybrid solar and biomass power plant is an extremely promising energy system and is likely to provide a major share of renewable bulk electricity production. Taking this into account, the government of India is creating biomass policies to minimize biomass feed stock in the hybrid power plant for establishing the market. The energy demand for cooling and process heat applications are increasing continuously due to increasing industries, office campuses, and institutions demanding results requiring huge amounts of electricity. Globally, in the industrial sector, about two-thirds of total consumption of energy is used for process heat applications. This increasingly huge amount of electricity demand results in higher consumption of conventional energy, for example coal and fossil fuels, which results in increasing greenhouse gas (GHG) emissions and the negative impact of climate change in this country. Presently, these industries either buy power from the state electricity boards or generate their own power largely. Finally, to reduce their net power consumption, some of industries produce power, as well as process heat, for their use through cogeneration. Although cogeneration is playing as advanced technology for generation of both electricity and process heat application, it is not possible to provide more than two such outputs, like space cooling and water desalination, for their requirement. To reduce energy demand and provide more than two such outputs like cooling and water desalination using different reject heat sources, a new concept of polygeneration processes has been developed in hybrid solar-biomass power plants. The modeling, simulation, and optimization of polygeneration hybrid solar and biomass system for power, cooling, and desalination and, for the economic aspect, cost analysis are discussed in the Chapter 6 of the book. In the polygeneration process, simultaneous production of power, cooling, and desalination from different heat sources in hybrid solar-biomass systems with higher energy efficiency takes place. It is one of the solutions to fulfill energy requirements from renewable sources and helps in the reduction of carbon dioxide emissions. The turbine is designed so that condensation heat of a power plant can be input for vapor absorption refrigeration (VAR) and condensation heat of a VAR cooling system is used as a heat input source for the desalination system. The VAR cooling system operates using the extracted heat taken from the turbine and condenser heat of the VAR cooling system and is used in the desalination system for production of drinking water per demand requirement. Though the production of electricity decreases due to extraction of heat from the turbine for the VAR cooling system and the evaporator load decreases due to heat taken from the condenser of a VAR cooling system for desalination, the complete system meets the energy requirements and increases the overall performance and PES. The technical modeling and thermodynamic analysis (energy and exergy) of polygeneration processes in HSB thermal power plants for combined power, cooling, and desalination has been analyzed. Specifically, the energy and exergy analysis are taken to better understand the performance of the polygeneration process in a solar-biomass hybrid system. The optimization of the polygeneration process in a hybrid solar thermal power plant has been done in this chapter of the book. Various scenarios are examined parametrically in order to present the system performance for various operating conditions. In this section, optimization using EES software (genetic method) is conducted with respect to the aforementioned analyses and utilized to compensate for the shortcomings of traditional objective approaches by allowing a larger perspective and determining a more complete spectrum of solutions. The results and discussions of the system are discussed in Chapter 6 of the book. It is observed that the heat input sources from solar and biomass technologies are very important for improving the overall efficiency of systems and these supplement with each other. From this study, it becomes apparent that the heat utilization from solar and biomass technologies are considered to be 37% and 63%, respectively, for modeling of an HSB system in the polygeneration process. The evaporator load and output of distilled water continuously increases at a faster rate up to a generator temperature of 150 °C. Thereafter, the rate of increase in the evaporator load and output distillation declines with increase in generator temperature while keeping other parameters of the system constant. For better understanding the effect of generator temperature on cooling load and desalination water output, we should concentrate on the effect of temperature on work output, VAR cooling, and distilled water output. The optimization of the proposed system has also been carried out for increasing the energy efficiency, VAR cooling load, output of desalination system, and total output. Though the production of electricity decreases due to extraction of pressure from turbine, the complete system (combined power, cooling, and desalination) meets the energy requirements and its overall efficiency increases.

This textbook should provide the researcher, student, and engineer with the intellectual tools needed for understanding new ideas in this rapidly emerging field. A new concept on polygeneration is included for the use of the engineering and science student. The book is also intended to serve as a general source and reference book for the professional (consultant, designer, contractor, etc.) who is working in the field of solar thermal, biomass, power plant, polygeneration, cooling, and process heating and the teachers teaching courses in solar thermal tehnologies.

I express my deep gratitude to Shri Sudhir Kumar Singh, Dr. Arun Kumar Tripathi, Prof. Hari Prakash Garg, Dr. Pradeep Chandra Pant, Prof. Rajesh Kumar, Dr. Chandan Banerjee, Mr. Sanjay Kumar, Dr. M.R.Nouni, Mr. Ramayan Singh and colleagues of the National Institute of Solar Energy (NISE) for their continuous inspiration and support during this work. I would like to thank to Mr. Lokesh Rana, Mr. Sunil Kumar, Mrs. Anju Singh, Mrs. Alka Solanki, Mr. Vikrant Yadav and Mr. Senthil Kumar for many discussions held during and after normal work hours on various nuances associated with certain systems and design work.

Special thanks to my brother Rakesh Ranjan Sahoo for helping in drafting and encouraging me to work on this manuscript rather than playing chess or watching TV.

Finally, I would like to thank my family for the patience they have shown during the lengthy period required to write this book.

Dr. Umakanta Sahoo

National Institute of Solar Energy

Chapter 1

Introduction

The energy scene in the world is a complex picture of a variety of energy sources being used to meet growing energy needs. However, there is a gap in the demand and supply position. It is recognized that decentralizing generation based on the various renewable energy technologies can help in meeting growing energy needs. Renewable energy landscapes in India during the last few years have witnessed tremendous changes in policy framework with accelerated and ambitious plans to increase the contribution of renewable energy such as solar, wind, bio-power, etc. Concentrated solar thermal and biomass powers have good potential for power generation and/or process heat in the industrial sector from renewable energy.

The launching of the Jawaharlal Nehru National Solar Mission (JNNSM) symbolizes both and indeed encapsulates the vision and ambition for the future of solar energy in India. The cost of power produced from Concentrated Solar Power (CSP) is becoming competitive with conventional energy sources with the development of technologies [1].

As capacity of CSP with heat energy storage is growing rapidly, hybridization with CSP is receiving more attention due to low levels of insolation in this country. The demand for biomass is increasing for use as solid fuels, such as wood pellets. It is the power generation potential of biomass, however, which has recently attracted greater attention. On the other hand, biomass power plants should have a secured supply of the required quality and quantity of biomass resources at a competitive price for sustainable operation of the plant. The cost of biomass resources has been slowly increasing due to non-availability of feed stock at the right price in recent years, so biomass and solar resources are important and supplement and complement each other for hybridization for continuous power generation.

Solar-biomass hybrid systems could be a viable reliable option for meeting energy demand in the industrial sector. In hybrid systems, solar energy can be optimally utilized in regions of high direct normal solar irradiance and where the biomass is available in abundance for supplementing and complementing each other in a cost effective manner. Solar thermal technology drives the thermal power system in peak sunshine hours and biomass heat drives in short transient periods during the day and at night time to generate constant power.

The energy demand for cooling, process heat, and desalination applications is increasing continuously in industry, office complexes, institutions, hospitals, residential areas, shopping complexes, etc. This is, at present, being met by conventional electricity, thus increasing the load on the grid and causing environmental pollution. Globally, in industrial sector, about two-thirds of the total consumption of energy is used for process heat applications.

The world’s huge and growing population is putting a severe strain on all the natural sources of the countries. Most of the water resources are contaminated by sewage and agricultural runoff. India has made progress in supplying drinking water to people, but gross disparity in coverage exists across the country. In India, access to drinking water to different communities and states has increased in the recent past, but as per estimation of World Bank, about 21% of communicable diseases are related to unsafe water supply. Ground water is the major source of drinking water in our country with 85% of the population dependent on it [2–3]. It is true that providing drinking water to such a large population is an enormous challenge.

Presently, most of the industries either buy power from the state electricity boards or generate their own power largely for end use applications like industrial production of materials and goods, office works, communication, cooling, and desalination. In India, the increase in huge electricity demand for industry, institutions, office complexes, commercial establishments, etc. has resulted in a higher consumption of conventional energy, as well as increasing greenhouse gas (GHG) emissions and is responsible for the negative impact on climate change. The process heat requirement is more than 67% of total energy consumption at a global level and about 50% of this heat requirement is for temperatures lower than 400 °C. At present levels, about 40% of primary energy consumption of the industry is contributed by natural gas and contribution from petroleum is about 41% [4]. Some of industries, through cogeneration, produce power as well as process heat for their end use applications to reduce their net power consumption. Cogeneration systems can reduce the grid electricity demand of the residential sector for lighting, space heating, and cooling and hot water, thus reducing greenhouse gas emissions.

Cogeneration is considered advanced technology for the generation of both electricity and process heat, but it is not possible to provide energy for more than two such outputs like space cooling, water desalination, and/or process heat for their requirements. However, polygeneration processes can meet full energy demands such as power, space cooling and heating, and process heating, including desalination. Polygeneration processes in hybrid solar thermal power plants can improve overall efficiencies (energy and exergy) and reliability.

1.1 Global Scenario on Renewable Energy

Renewable energy is one of the options to transform the energy system to make it less carbon intensive, sustainable, meet climate change goals, and bring energy security benefits. Renewable energy encompasses a broad range of energy resources and technologies that have differing attributes and applications. Renewable energy resources include solar energy, bioenergy, geothermal, wind, and hydropower. These sources are abundant and widely distributed, but they are not equally easy to harness. Solar, biomass, and geothermal resources are for generation of electricity, water pumping, and process heat applications. Hydropower and wind resources are only for the generation of electricity and water lifting and bioenergy resources are utilized for electricity generation and in transport sectors. Renewable energies are the world’s second largest source of electricity generation after coal based power generation plants. These sources have huge potential in meeting energy requirements for process heat in industry and transport sectors. For the first time, the renewables industry has achieved a major milestone in 2015 with capacity additions exceeding as compared to fossil fuels and nuclear energy [5]. The total renewable power capacity reached 1,849,000 MW (including hydro power) at the end 2015 [6]. Of this