Now, with regard to economic policies of the government to make subsidies targeted and increasing energy prices and the increasing importance of finished fuel costs of all domestic products as well as the support of the Ministry of Energy of the construction of electricity production units at small-scale by natural or legal persons have caused managers of industries to try to save even more in energy consumption, and sometimes try to establish small-scale electricity to power plants.
In complexes, major energy consumers include:
Internal combustion engines
Burners
Energy use optimization in engine and burners:
Setting pressure of fuel pump
Cleaning or replacing the fuel injection nozzle
Continuous control and setting of fan or air damper and if available timely replacement of air filters
Compliance with fundamental issues above reduces the noticeable fuel consumed.
Another topic that is important in the scale of the country is increasing fuel efficiency in consumer systems. For example, burner efficiency is approximately 80% that with setting the proper amount of good weather and fuel injection, its efficiency can increase up to 98%. Certification and standardization organizations in the country should pay attention to it.
For example:
Efficiency of a gas power plant is about 31% to 366% in ideal conditions of turbine, compressor, hot air furnace and the rest of the energy about 64% to 69% is hot gases, which gets just outside through the chimney. By placing hot water or steam convertor, the efficiency can be raised from 31% to 36% to 70% to 78%, if the percentage of these units is converted into energy. If we change the above percentages to energy units, the savings will be more palpable. For example, in an industrial town where the average energy consumption efficiency is 50%, fuel consumption of this industrial town is equivalent to ten fuel trucks with a total capacity of 280000 liters.
The energy from liquid fuel is approximately 2800 Mega kcal, of which only 1400Mega kcal it useful and the rest is discharged from chimneys and body of machinery. For every one percent increase in efficiency, we will have 1,400 liters savings. If we can increase the efficiency of the complex up to 70%, we will have 28,000 liters save a day.
Saving issue has a longer history in developed countries. Perhaps as old as the invention of the boiler, this then allowed the workers to be warm with heat from the chimney.
Due to the importance of this, one branch of mechanics is dedicated to this issue called Combind Heat & Power, or briefly called CHP.
CHPP Science is progressing due to savings in per capita energy consumption and contribution to the cleanliness of the environment, and in some cases to prevent the pollution of air and also considerable use of clean energy.
For example, by spending a lot of money, modern man receives heat and solar energy by the solar cells, while tens of times of it is wasted by the exhaust and chimneys. Therefore, along with the use of clean energy using heat chimney also contributes to nature.
Where can the heat we take from the chimney be used?
The life and work space heating
Steam generation for industrial applications or steam power plant (combined cycle)
The hot water production buildings and offices and factories.
The hot air furnace production
Using hot air for drying fruits
Using smoke and exhaust heat of internal combustion engines for generator sets Absorbtionn to produce cold air in the summer.
Receiving electricity energy (power) of the semiconductor stacks temperature thermocouple (If we tie two metals with the opposite material from one end and put to the heat, on the other end voltage difference comes up and this voltage difference increases linearly. With making these thermocouples series, one can reach acceptable voltage to light up the area at night)..
Limitation of the use of hot air of the chimneys:
The limitation of temperature of heat exchanger, the converter that receives its heat from the flue and combustion products from a predetermined operating temperature limit. This determines the limit of use of smoke.
For example: If you intend to place the boiler with working pressure of 10 atm on the vent path, steam saturation temperature will be 1800 degrees and at least 20 to 30 degrees Celsius converter exhaust smoke should be higher. So the output of the converter and finally chimney will be limited to 230 ° C.
The restriction of dew point:
When the steam temperature is lower than the dew point temperature, water vapor condenses and sulfur or CO22 in the fuel and smoke produces acid with low PH that causes corrosion in the chimney wall adapter or subject, and the designer must consider smoke temperature in designing and determine flue material due to corrosive gases.
The furnace pressure drop:
The most important thing in the use of CHP converters is fuel pressure drop.
When the heat loss gas pressure increases causes loss of electric power to compensate for this failure, and some fundamental flaw is created in burners fan or compressor. The amount of air is designed to reduce the air has decreased significantly resulting rise in temperature of flame or smoke and NOX emissions, which are harmful to the environment.
Extensive discussions have been raised on this issue that will be dealt with in its place.
For example, why do we not increase efficiency from the beginning not to use waste heat?
The fact is that in many processes, there is no practical possibility of raising the efficiency directly. To raise the efficiency of a steam power plant, it is acted as follows.
Increasing turbine inlet steam temperature
Decreasing pump inlet water temperature
If we assume that all plant equipment including the boiler – turbine – pump condenser works with 1000% efficiency, the ideal efficiency of the plant is:
μ= (Steam temperature in Kelvins) / (water temperature in Kelvin – steam temperature in Kelvin)
The highest temperature to which steam can be increased is 370 ° C or 273+370=643 Kelvin and the minimum temperature that is economic is environment temperature. If in winter the condenser temperature is decreased to 7 ° C or 273+7=280 Kelvin, the highest efficiency of this power plant in efficiency equal to 100% of individual components is:
Achieving optimal efficiency requires a pump working at 210 atmospheres or a metal that at high temperature withstand high pressure that will be very expensive. Thus, where there are price and efficiency constraints, we have to choose another way, and one of these ways is CHP.
Definition of CHP:
Simply put, coping with the nature and the combined use of heat and power in a heating system is called CHPP, and for any space and location, it requires a special use that designer should see.
Using concrete experiences, concrete examples are expressed for the design:
The use of exhaust heat of the boilers for residential buildings:
A) Boiler: the boiler smoke can be used for the hot water of the complex and in the summer supply hot water of observation or in winter to melt snow of the roof.
B) Hot water boiler: to melt snow in winter and supply major amounts of hot water of the complex by placing a larger reservoir and supplying hot water of the greenhouse of complexes and even supplying hot air and even steam for the bath complex.
The industrial boiler
A) With a capacity of less than 5 tons
Industrial and sanitary hot water production
Preparing clean warm air to heat the environment
Preheating (economizer) of the input water
B) With a capacity of more than 5 tons
Uses similar to rows (1) in addition to creation of a boiler of hot water
Increasing inlet air temperature of the boiler
c) Pot of hot oil
Used for space heating
For cooling Administrative Affairs in summer
The creation of a small boiler
Production of hot air for special applications
d) Hot air furnace
The output of warm air furnaces is usually a high temperature. This is because in these devices and systems of hot oil as working fluid is used at high temperatures, exhaust temperature will increase, which is operated as follows.
Used for space heating
In the summer for cooling administrative affairs and in places needed
Hot water preparation for the plant
Steam production for specific purposes (e.g. Steam iron)
Hot air production at low temperature for dryers and so on
Preheating boiler feed water if there is any
Desalting water for areas that do not have healthy water
Food manufacturers can use it for raw material drying.
Power Plant
CHP main argument is mostly for power plants for building small plants up to 255 MW is currently widespread and the government is willing to buy surplus power produced by these companies. If the energy wasted by these plants is not used, these power plants become uneconomical. Currently, methods to use waste energy of these power plants are of utmost importance, so it is necessary for dispersed electricity producers to become aware of these ways.
Small power plants are of four main forms:
Steam turbine
Gas turbine
The internal combustion engine
The combination of steam and gas turbines
Steam turbine:
The water is pumped with high-pressure to the boiler. In the boiler, the water evaporates and the vapor temperature is taken to beyond saturation and superheated is produced. The dry steam enters the turbine and a steam turbine electrical generator rotates by that and the output is power accordingly, condenser and distillation is then pumped back into the cycle.
It is better to use BACK PRESSUR turbines at these plants because the output of these turbines has pressure and can be sent to a plant that needs low pressure steam and then output collects steams and returned to the pump. This topic has short or long fine points that can be collected in a book.
Gas turbines:
Gas turbine is like a jet engine. First air is pressured by compressor into the combustion chamber, and fuel or gas is directed into this room burns with air and produces hot and enters a gas turbine and moves its blades and when exits the turbine, its temperature is about 600 to 800 ° C.
This hot air is very energetic and of its advantages is the low ratio of carbon dioxide to oxygen, and we can say it is hot gas but clean.
Of the disadvantage of this type of plant is requiring compressed natural gas.
Combined Cycle:
If the turbine exhaust gas enters converter that produces superheated steam and superheated steam enters the steam turbine, power plant will be combined cycle then.
Combustion engine power plant:
This type of plants can be called the first scattered power plant, a gasoline or diesel fueled internal combustion engine and a generator driven recently brought into circulation and natural gas produces electricity.
The wasted energy of these engines can be used in two points. The first is using heat of engine oil that is grabbed by fluid water and other gases resulting from combustion that have a temperature of about 400 to 600 ° C. The important thing in combustion engines with natural gas is hotter emissions temperature compared to gasoil.
The efficiency of these power plants is generally 30 to 40 percent. This means that for every 100 kilo and or cubic meters, 30 to 40% of it is useful energy and the rest is wasted. In using wasted energy of each of these plants, there are several methods.
For clarification and easier understanding of this energy, we state a few examples.
Every cubic meter of natural gas produces heat of 8500 to 9500 kcal.
A household gas heater burns 0.8 to 1.2 cubic meters of gas per hour.
On average, each gas heater uses 10 kW of power.
Person hot water intake per day is equivalent to burning of 0.2 cubic meters of fuel.
The average number of each Iranian family is 5 persons.
The average gas consumption in Iran to produce healthy hot water is one cubic meters per family.
Each ten meters from a residential home in the winter in cold areas needs 0.15 cubic meters of gas per hour.
Each 1000 kW (one megawatt) power produced by plants consumes 250 to 320 cubic meters of gas.
Every 10 kilowatts of power needs 3 cubic meters gas cubic meters of gas, and 1 cubic meter of it transforms into useful electricity and two cubic meters are wasted.
Of two cubic meters of gas wasted, 1.5 cubic meters can be easily recycled.
Of the wasted power of a one MW power plant building heating and hot water consumption of 150 families can be provided.
The cool air (air conditioners) of 1000 apartments in hot areas can be provided.