Geothermal energy is a natural thermal energy which is developed from the earth’s crust using current technical and economic conditions. This energy comes from the lava inside the earth and exists in the form of heat. The temperature inside the earth passes through the flow of groundwater and the lava flows to the crust 1 to 5 km above the ground, and the heat is transmitted to a place closer to the ground. High-temperature lava heats nearby groundwater, which eventually oozes out of the ground.
The easiest and most cost-effective way to apply geothermal energy is to take these heat sources directly and extract their energy according to different geological conditions.
Generally speaking, for the shallow type of relatively economical geothermal resources, especially the use of geothermal resources of about 200m underground, it is mainly applied to the water source heat pump technology, and the deep subtype economic geothermal resources are mainly used for power generation, heating, hot springs, tropical plants and aquaculture.
The geothermal heating utilization rate
The geothermal water is recharged after the temperature of the heating system is lowered, and the geothermal water recharge temperature directly affects the utilization rate of geothermal heating.
Geothermal heating utilization rate = geothermal actual heat supply / geothermal heat supply
To improve the geothermal utilization rate, it is necessary to reduce the drainage temperature. The more heat that the geothermal water can extract after the drainage temperature is lowered, the larger the heating area.
However, in actual heating, there is a limit to lowering the drainage temperature. If the drainage temperature is too low, it is necessary to increase the cooling system of the heating system and increase the investment in indoor facilities. Therefore, the rational development of utilization plans is the key to improving the utilization of geothermal heating.
At present, the combination of the radiant heating method is floor radiant heating along with water source heat pump peaking. The practice proves that the energy saving effect and the economic benefit are very good.
Geothermal energy problems and solutions
Geothermal heating generally adopts the method of “extraction and irrigation”, which is to use the thermal energy of geothermal water to make use of heat without water consumption.
Usually, after a geothermal well is made, its water temperature and water consumption are certain to some extent.
The most common way of geothermal heating is to expand the heating area by the cascade utilization of geothermal water to meet the heating requirements.
In geothermal heating, it must be considered that the thermal load provided by geothermal water is used as the basic heat load to meet the heating requirements of the initial cold period and the end cold period. In the severe cold period, the basic heat load cannot meet the heating demand.
Moreover, geothermal water contains minerals and trace elements, which are corrosive and may cause corrosion of metal pipes.
Cold season heating
It should be required to provide the corresponding peaking heat source in the scheme formulation to supplement the insufficient heat load. Further digging the potential of the tailwater, and usually adopting the heat pump peaking scheme, which not only can further reduce the geothermal tail water temperature to achieve the cascade utilization of geothermal water, but also improve the utilization of geothermal heat.
Pipeline corrosion problem
This problem should be fully considered when selecting equipment for geothermal stations. In particular, the heat exchange station equipment should use titanium plate heat exchangers, and non-metallic pipes should be used for pipes conveying geothermal water to avoid pitting corrosion. Or indirect heat exchange technology can be used, then the geothermal water pumping system and the heating cycle system can operate independently, which can effectively solve the problem of pipe network and end corrosion.
End heating ways
For the different heating grades of traditional radiators and new floor radiant heating, through the technical method of geothermal cascade utilization, the geothermal energy is used hierarchically and hierarchically, and the heat of geothermal tail water is extracted by heat pump technology to reduce the recharge temperature, which can effectively improve the thermal energy utilization efficiency.
Geothermal energy heating equipment
The submersible pump of geothermal well is often called deep well pump. It is the key equipment in geothermal heating. The choice of maintenance and operation is related to the stability of geothermal heating system, so it must be highly valued. Unlike other pumps, deep well pumps must meet the characteristics of high temperature resistance, corrosion resistance and durability in geothermal heating.
At the same time, it must meet the requirements of flow, lift and so on. Therefore, it must be selected according to the following conditions when selecting:
- The flow-depth curve of a single well.
- The dynamic and static water level of well water.
- The temperature of the geothermal well.
- External pipe network resistance
For the selection of geothermal heating and heat exchange equipment, the following issues should be noted:
- Geothermal water is used in the geothermal heating system. It is corrosive, so corrosion-resistant heat exchangers such as titanium plate heat exchangers or copper alloy heat exchangers are often used when selecting heat exchangers.
- The number of heat exchangers should be greater than 2, and the parallel connection is optimal. It is convenient for the heat exchanger to be repaired in time when there is a problem in the use process.
- Considering the number of heat exchangers and the heat exchange area for the heat dissipation method of the terminal, the extra 10% to 20% level should be increased to meet the heat exchange effect of the low temperature hot water.
- The intermediate heat exchanger is installed in the heat pump peak shaving system. The number of heat exchangers to be replaced is preferably two.
- When adopting the plate heat exchanger, detailed calculation should be carried out according to various parameters, and the type with high heat exchange efficiency and easy maintenance should be selected, and the height of the plate should not exceed 1.5 m.
Geothermal heating prospects
Geothermal resources are characterized by cleanliness and environmental protection, and are extremely valuable resources. When using geothermal resources, attention should be paid to their protection so that geothermal resources can be used sustainably. At the same time, it is necessary to continuously strengthen the development and research of geothermal heating related technologies, so that geothermal resources can be more fully utilized by the society and create wealth for our society. When developing geothermal resources, you should also do the following:
- Improve the development and utilization of geothermal resources to avoid the random exploitation and over-exploitation of geothermal resources.
- Accelerate the research and development of new technologies and processes for geothermal heating.
- Strengthening technical cooperation.