In enterprises of various capacities, the availability of stable electricity is extremely important. Due to the huge amount of electricity consumption, it is not profitable to use the central mains. More often it is required as an additional source. At the same time, it is not available in all regions. In many cases, enterprises and production facilities are built in some distance from cities, and therefore the question of providing electricity in the required volume is acute. As a result, the question arises as to whether a gas piston power plant or a gas turbine power plant is better.
Gas piston and gas turbine plants: description
1. Gas piston power plant is a power generation system with a reciprocating internal combustion engine. It can run on either natural gas or another type of combustible gas, depending on the model and manufacturer. During operation, the plant generates two types of energy simultaneously (cogeneration): heat and electricity.
A gas turbine power plant also operates on the principle of cogeneration, producing electricity and heat at the same time. The plant uses one to several gas turbine engines, which are connected to an electric generator. At the same time, all equipment is united by a common control system, forming a single energy complex.
2. A gas piston generator works like an internal combustion engine: the unit burns fuel, which expands, thus transferring energy to the piston. From this, the crankshaft begins to move, transferring energy to the generator.
A gas turbine engine uses air with gas to work. When they mix, fuel is formed, which is subsequently burnt. As a result, the gas under pressure transfers energy to the turbine blades, driving the shaft itself.
3. The essential difference between these units is inertia. When the piston by inertia passes the dead centre, it returns to its initial position, after which the moment of overload occurs. Although the blades are subjected to gas loads, turbines have no inertia. Due to this, the number of revolutions of the crankshaft is increased.
4. Gas turbine engines, despite their higher power, have a slightly lower efficiency. This is due to the dissipation of energy, which is produced by the gas, during the operation of the turbines. At a certain point, the loads become maximum, resulting in a lower operating life after each stop/start of the unit. Gas piston engines don’t have this problem.
Criteria for plant selection
Various plants can be used to generate electricity and heat in a company and production facilities. Here it is important to consult expert engineers who will help to make the necessary calculations and develop a project for the set goals. You can find out more about this from our manager.
The main criteria for selecting units are as follows:
1. How easy the unit is to use.
2. How maintenance and repairs are carried out.
3. Where the unit should be repaired.
4. What is the fuel consumption.
5. How much cost will be required for use.
6. How long it will take for the installation to pay for itself.
There are a huge number of models on the market. Therefore, it is important to find out which one is best suited to your business. This requires the help of engineers and experienced experts.
Operational costs of the plant
Every machine needs to be treated with care. Over time, it breaks down and repairs are required. Thus, the cost of overhaul of a gas piston engine can reach 30-35% of the original price of the equipment. The overhaul includes replacement of the entire piston group. The overhaul is performed directly at the company every 7 years. It doesn’t require complex diagnostics or specialised equipment.
The cost of gas turbine unit restoration may cost 30-50% of the original price. At the same time, it is often impossible to repair the unit without removing it from the facility, as the unit has significant technical difficulties. For the procedure, the supplier removes the broken unit and brings in a replacement. The old unit is restored exclusively in factory conditions.
Features of operation
For autonomous gas turbine power units, industrial turbines are used. They are capable of operating continuously at different load indicators.
The minimum permissible electrical load, officially declared by the manufacturers of industrial turbines, should be within 3-5%. However, in this mode, gas consumption will be significantly increased – by 40%. At most, they are able to withstand short-term intervals with a load of 110-120%.
Gas piston power plants are characterised by significant economic efficiency, providing extremely high electrical efficiency. The nuances arising from minimum loads can be resolved at the project development stage. We can take into account all the nuances in the design, ensuring stable operation of the system under almost any conditions.
By following the manufacturer’s recommendations on the operation of the gas piston plant, it is possible to significantly extend its service life. At the same time, the owner will be able to save money on repairs. In rare cases, several electric boilers are included in the design to bring the gas piston plant to nominal operation at partial loads. They provide the required 50 per cent of the load.
When designing autonomous power plants with gas piston engines and gas turbines, it is optimal to follow the “N+1” rule, where N is the number of operating units. An additional one will act as a reserve. This will help to ensure power generation even if one unit is under repair or maintenance, without loss of power.
Dependence of unit power on ambient temperature
During a strong increase in ambient temperature, the power of the gas turbine unit will drop. At the same time, if the temperature decreases, the power will increase. According to ISO standards, it is measured at +15℃.
The gas turbine unit can give out 1.5 times more heat compared to the gas piston system. When using a powerful stand-alone CHP unit in the utility sector, this becomes a key aspect of selection. Especially if a large and uniform consumption is required.
Due to the significant outlet temperature of gas turbine units, a steam turbine can be utilised. This is required if the maximum amount of electricity is to be generated with an equal amount of gas input. This results in a high electrical efficiency of up to 59%. However, an energy complex in this design will not only be more difficult to use, but will cost 30-40% more.
The efficiency of the plants
One of the important criteria showing what is better – a gas piston power plant or a gas turbine power plant – is efficiency. It also has an impact on gas consumption. On average, per 1 kWh, the fuel consumption of a gas turbine unit is lower than that of a gas piston unit. However, the latter is highly undesirable for long-lasting loads of less than 25 per cent.
The completeness of combustion must also be taken into account here. When the fuel is burned, the main work – the rotation of the electric generator – takes place. The remaining energy is converted into thermal energy, which can also be used in the enterprise. In such a situation, the efficiency will be already 80-90%. Note that if the load of the gas turbine plant is reduced to 50%, the electrical efficiency will drop.
In addition, turbines need high inlet pressure, which requires the installation of compressors, resulting in increased fuel consumption. When comparing turbine and reciprocating systems, it is shown that the use of turbines is only appropriate for linear heat and electricity requirements that do not exceed 40 MW.
A gas piston system consumes 25-30% less gas than a unit with turbines. Accordingly, with similar parameters of equipment and their cost, it is more favourable to use piston units. We can advise you more about it. Call us on the phone numbers listed on the website and we will answer all your questions.
Environmental impact of plants
An important consideration in design and selection process is the environmental pollution from the operation of an autonomous power plant. Piston units in this matter are inferior to gas turbines, because when burning out engine oil, there is a slightly greater emission of toxic substances. However, the indicators are not critical.
You can ask the SES for the background level of the MPC, where the autonomous power plant will be located. In addition, a calculation of dispersion is made with the condition that the emission of toxic substances does not provoke the growth of MPC. The necessary height of the chimney is calculated to ensure compliance with SanPiN (Sanitary Regulations and Standards). Note that with a power of 16 MW, NO2 emissions are not critical: if the chimney is 30 m, the MPC will be 0.2, while at 50 m, it will drop to 0.1.
It is also worth considering the production of vibrations and noise from the installations. Both produce noise within a certain frequency range. However, this problem shall be addressed by appropriate engineering surveys. Here, an additional acoustic calculation is made to determine compliance with SanPiN requirements.
Conclusion
In the case of even loads and the “N+1” rule, gas piston units can be the main source of energy supply in a company. However, it is also necessary to install standby units with tanks for additional fuel, i.e. diesel. For capacities up to 50 MW, the use of reciprocating engines is fully justified. Along with this, the consumer can completely abandon the external source of power supply. However, in such a situation, it is necessary to take into account absolutely all the nuances. Piston generators can also be used as a backup or emergency power supply source.
Gas turbine units can be used for loads of 14-15 MW. However, significant fuel consumption will not be justified. It is better to use these units at capacities of 50-70 MW.
The service life of both units is relatively equal. If the scheduled maintenance schedule and step-by-step replacement of spare parts are observed, the systems can withstand 200 thousand motor-hours in case of gas turbine units and over 200 thousand in case of gas piston units.
Be sure to consult our specialists when choosing power units for your future autonomous power plant. They will also be needed during construction and start-up. Our company has sufficient experience and a large number of implemented projects with gas piston plants.