DISTRIBUTED GENERATION AND COGENERATION

Today, energy is the most strategic human need. Meeting energy needs has become a real permanent concern for all countries. A glance at current state of depleting fossil fuels on the one hand and its damaging impact on the environment on the other, optimized methods of energy generation and conversion of fossil fuels gain importance. As one type of such converted energy, electricity plays a crucial role in energy basket of countries. Major part of electricity generated around the world converting fossil fuels. More than 80 per cent of electricity used in Iran is generated by gas and steam turbines of thermal power plants. Thus, given the finite nature of fossil sources, the issues of finished price of energy, reducing the impact of energy consumption on the environment, reducing energy loss, and improving efficiency in thermal electricity generation gain due importance. Raising efficiency is achieved through different ways.
Along with improvements in facility design, two other approaches are popular in current global electricity industry, namely:
1. Reusing residue produced in thermal electricity generation, or heat and electricity cogeneration;
2. Transferring generation units to utility grid or distributed generation.
As a pioneer in electricity generation company, MAPNA Group has taken preliminary steps in distributed generation and cogeneration (CHP) markets thanks to its unrivalled technical, engineering, financial, and management capabilities, and excellent record in procurement of facilities in power plant projects, and out of a call of duty in protecting fossil fuels as invaluable national resources, and in reducing energy losses, along with its social responsibility, abandoning motives of material gain. MAPNA Group works to attend a duty which society, posterity, and its shareholders have assigned to the Group.
 
COGENERATION (CHP) AND DISTRIBUTED GENERATION (DG)

DISTRIBUTED GENERATION

In common practice, electricity needed for consumers including industrial, commercial, agricultural, and house utilities is generated by centralized and large power plants and distributed to consumers; in distributed generation, small power plants are built in the vicinity of consumer centres to provide the electricity to utilities. The energy loss of total electricity generated by large-scale power plants is as follows:
TYPE OF LOSS     PERCENTAGE (%)
Electricity plant insider use
۴
Electricity transmission network
۴/۵
Electricity distribution network
۱۷/۵
Total ۲۶
As given in the table, 26 per cent of the generated electricity is wasted in centralized method during transmission and distribution.
A recent report by Ministry of Energy indicates that more than 30 per cent of a total electricity loss occurs in summer peak. Thus, a shift of strategy from centralized generation to distributed generation is a decision critical and strategically important.

ADVANTAGES
 

  • Facilitated generation of emergency electricity;
  • Reduced costs of transmission and distribution;
  • Improved efficiency in electricity industry.
  • Reduced loss in transmission and distribution;
  • Improved sustainability, safety and energy provision quality;
  • Diversified fuel sources and increased efficiency;
  • Reduced investments by government and facilitated private sector participation;
  • Reduced land ownership for network development, and its related financial, social, environmental drawbacks and pollution;
COGENERATION AND DISTRIBUTED GENERATION

COMBINED HEAT AND POWER GENERATION

In distributed generation, proximity to end users makes heat recovery and cogeneration of heat and electricity possible. In other words, distributed generation also helps with cogeneration.
Cogeneration is defined as generation, at the same time, of some types of energy (usually thermal and electrical) in a single unit in an integrated way. The system also generates cool air along with cogeneration of heat and electricity using outgoing energy, which is also called ‘combined cooling, heating, and power generation.’
This system enjoys added advantages of improved efficiency. Through this system, higher efficiency of 80 per cent is achievable.

CHP TECHNOLOGY

CHP systems incorporate different technology into its structure depending on the type of prime mover. Prime movers are categorized as the following:

  • Microturbine
  • Stirling engine
  • Fuel cell
  • Gas turbine

Solar, wind, and small-scale hydroelectric dams are also categorized as prime movers.

MAPNA EXAMPLE CHP UNIT

MAPNA’s example CHP, with a capability to be converted to CCHP, has the following components:

  • Chiller (optional)
  • Control system and related facilities;
  • Gas turbine;
  • Heat recovery generator;
  • Generator;
  • Desalinator;
GENERATION AND EFFICIENCY IMPROVEMENT PLAN

The unit gives the option of using part of steam by heat recovery generator or part of electricity by a chiller system to cool the incoming air to turbine. The system contributes significantly to turbine capacity and efficiency in hot seasons through decreasing the temperature to 15 degrees centigrade.

SYSTEM DETAILS

CHP in the initial stage of the generation cycle generates 25MW electricity in ISO conditions using fossil fuel and UGT25000 gas turbine (Ukrainian Zorya-Mashproekt) and Jisalt 245F (French Jeumont Rouen) generator.
Through channeling gas exhaust of the turbine with output rate of 87kg/s and temperature 480 degrees centigrade into a heat recovery steam generator (HRSG), generation of 48 tone/h steam with relative pressure of 12 atm and 200 degrees centigrade becomes possible.
The steam then could be used in different applications. In MAPNA’s example CHP, the steam generated thus is used in a water desalinator facility, which produces about 104lit/s (9000 cubic meters of water per day) of desalinated water. Estimated total output of this CHP system under ISO conditions is about 80 per cent.

SPECIFICATIONS OF GAS TURBINE

Turbine is critical in cogeneration of heat and power. In this system, the surrounding air is guided to air filters and then to compressor to be compressed according to different ratios. The next step is combustion of the compressed air and fuel injected, which releases energy. This energy helps turbine axis rotate, thus producing mechanical energy for generator. Along with this, the hot gases coming out of the turbine is channeled into recovery steam generator for further use. MAPNA’s example CHP uses UGT 25000 (DG80) through an agreement contract with Ukrainian Zorya-Mashproekt to transfer of technology of manufacturing 42 turbines.

Technical and thermodynamic specifications of this turbine under ISO conditions are as follow:

  • Rated Power 25MW
  • Electrical Efficiency 35 per cent
  • Exhaust Gas Mass Flow 87kg/s
  • Exhaust Gas Temperature 480 degrees Celsius
  • Pressure Ratio 1 to 22.6
  • Dimensions 2.5 in 2.5 in 6.5 (m)
  • weight 16 tons
  • Gas Turbine Output Shaft Speed 3000rpm

SPECIFICATIONS OF SYNCHRONIZED GENERATOR

Generator is responsible for generating electrical power in a certain frequency a voltage rate. Mechanical power of the turbine shaft is transmitted to generator shaft by a coupling shaft. The DC current connected to the rotor coil creates a 3-phase voltage to stator winding. In synchronized generators the frequency of the machine is proportionate to the rotating speed of the coupling shaft. MAPNA’s example CHP uses Jisalt 245F generators made by French Jeumont Rouen, the technology of which has been transferred to MAPNA by an agreement contract.
Technical specifications of the generator are as follow:

  • Rated Continuous Output 25
  • Rated Nominal Voltage 11 KV
  • Rated Frequency 50 (HZ)
  • Rated Speed 3000rpm
  • Dimensions 6.5 in 4.6 in 3.9(m)
  • weight 64.2 tons
SPECIFICATIONS OF ACS

Synchronization generator
CHP major systems in terms of control are generator and turbine system, heat recovery steam generator, water desalinator facility and auxiliary equipment. Other parts would also be present in a plant if it uses more than one such unit.
To prevent the system from entering a hazardous phase of function, the ACS (Automatic Control System) incorporates safety arrangements in compliance with acceptable standards.
An ACS is responsible for safety of a unit of CHP, which the following specifications:

  • HMI Software: WIN CC
  • Protection System of ACS is based on SIL-3-Certfied
  •  Software for Logic Develop: SIMATIC MANAGER STEP 7
  • Hardware : – CPU , – IO Module

The safety system takes the exciter, Automatic Voltage Regulator (AVR), and synchronization as part of ACR.

توابع اصلی
MAJOR FUNCTIONS ACS
ACS system functions in any unit to do the followings for main and auxiliary sections of turbine, generator, heat recovery steam generator, and water desalinator facility:
• Automatic control;
• Protecting the system against critical and hazardous conditions;
• Governing;
• Monitoring and supervision.
To achieve these functions, ACS uses its control, governing, SIL-3-based protection, and its Monitoring and Archiving and Data Gathering specific functions. Each of the above functions use their internal functions to achieve the objectives defined for them.
A Local Operator Panel is predicted to operate generator. An example of the network topology and ACS arrangement is given in the figure (on website).

HEAT RECOVERY STEAM GENERATOR

A Heat Recovery Steam Generator is installed to recycle the energy of outgoing hot gases from gas turbines. The steam generated thus is used in water desalinator facility. Reusing the waste heat as in CHP increases the efficiency of the whole system from 30 to 80 per cent. Heat recovery steam generator is designed by MAPNA Boiler Co. and South Korean partner Doosan. They are installed horizontally and with or without an auxiliary burner. The specifications of HRSC under ISO conditions are as follow:

  • Flue Gas Flow Rate 87Kg/s
  • Steam Pressure 12barg
  • Stream Flow Rate 47.8 Ton/hr
  • Steam Temperature 200 degrees Celsius

CHILLER

To improve power and efficiency of gas turbine and ultimately total efficiency of the system, cooling the air incoming to the compressor in ISO conditions up to 15 degrees Celsius in hot seasons becomes possible through a chiller system as provided by MAPNA’s example CHP. This innovation improves the gas turbine power about 7MW and efficiency as 3.3 per cent. Chiller system recycles part of steam generated by HRSG and part of electricity generated by gas turbine as its driver force. The rate of air incoming to compressor is about 87kg/s.

CHP

Since CHP recycles the steam generated by HRSG which reuses hot gases of the turbine, installing thermal desalination facility has advantages over membrane desalination process, which reduces costs for end users. The technology used is MED-TVC (Multi Effect Desalination and Thermal Vapour Compression). This technology works with lower temperature and pressure and uses lower electricity power. Along with these properties, it covers also the capacity needed by CHP.
In MED-TVC, sea water is ducted through condenser tubes. After receiving some heat, water is divided into two parts; major part which functions as cooler, returns to sea. The second portion is ducted to operator as feed. Evaporation process occurs in outer surfaces of heating tubes, with condensation occurring in inner surfaces. With increasing the steps thus, fewer vapour will be needed as input to system. To improve efficiency and to create vacuum, a compressor is used.
The capacity of the system is 9000 cubic meters per day (roughly 375 cubic meters per hour) production of fresh drink water. The system uses HRSG vapour, with using sea water as its feed. The product is used as portable drink water for household use. The temperature of salty water would be used as a heating source of incoming water. Part of water produced in the first step is returned back to HRSG to produce steam. Other technical specifications of the system are as follow:

  • Desalination Type: MED-TVC
  • Product Net Flow Rate/Unit 9000m3/day
  • GOR [product/inlet steam (mass ratio)] 8.5
  • Operating Steam Pressure 12 barg
  • Operating Steam Temperature 200 degrees Celsius
  • Effects Tube Arrangement: Horizontal
  • Guaranteed Product Water TDS (ppm): Less than 10
  • Steam Flow Rate/Unit: 47.8 Ton/hr