# Energy Engineering Questions and Answers – Hydrothermal Systems

This set of Energy Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Hydrothermal Systems”.

1. What is range of temperature at Hydro thermal reservoirs?
a) 350oC
b) 210oC
c) 50oC
d) 1900oC

Explanation: Hydrothermal resources are wet reservoirs at moderate depths containing steam and hot water under pressure at temperatures upto about 350oC. These systems are further subdivided depending upon whether steam or hot water is dominant product.

2. When do hydrothermal resources arise?
a) When the movement of tectonic plates occurs
b) When the area is prone to volcanic eruptions
d) When temperature on earth surface is very high

Explanation: Hydrothermal resources arise when water has access to high temperature rocks, this account for the description as HYDROTHERMAL. The heat is transported from the hot rocks by circulating movement.

3. How does the hot water or steam escape through earth surface?
a) Through fissures
b) Through Pot holes
c) From Wells
d) Through water bodies

Explanation: Hot water or steam often escapes through fissures in the rock, thus forming hot springs, geysers fumaroles etc. in order to utilize the hydrothermal energy, wells are drilled either to intercept a fissure or more commonly into the formation containing the water.

4. What is the range of depth of most Hydro thermal wells?
a) 600 – 2100m
b) 50 – 60 m
c) 8 – 10 km
d) 1200 – 5400m

Explanation: Most hydrothermal wells range in the depth from about 600 to 2100 m, although there are some shallower and deeper production wells. As already mentioned for practical purposes hydrothermal resources are further subdivided into vapor dominated and liquid dominated types.

5. How the steam after passing turbine is cooled down in the geo thermal energy plant?
a) Water cooled
b) Cooling towers
c) Air cooled (Blowers/ air vents)
d) Chemically cooled

Explanation: A direct system is used at the geysers in which the turbine exhaust steam is condensed by direct contact with cooling water. The resulting warm water is circulated through a mechanical draft cooling tower and returned to the condenser.

6. How much percent of Non-condensable gases are contained in steam?
a) 0.5 – 5%
b) 10 – 25%
c) 75 – 85%
d) 50%

Explanation: The steam contains 0.5 – 5% by weight of non-condensable gases which appear in the turbine exhaust. These gases consist mainly of carbon dioxide with small amounts of methane and ammonia, which are largely harmless in the quantities present.

7. The withdrawal of large amounts of steam from a hydrothermal reservoir may result in ____________
a) landslides
b) surface subsidence
c) light surface
d) loss of land fertility

Explanation: The withdrawal of large amounts of steam from a hydrothermal reservoir may result in surface subsidence. Such subsidences have sometimes occurred in oil fields and are dealt with injecting water into the ground.

8. What is the range of range of the water, which comes from degrees of salinity?
a) 300 – 8000 ppm
b) 4500 – 50,000 ppm
c) 70000 – 85000 ppm
d) 3000 – 280,000 ppm

Explanation: The water comes with various degrees of salinity, ranging from 3000 to 280,000 ppm of dissolved solids, and at various temperatures. There are, therefore, various systems for converting liquid dominated system into useful work that depend upon these variables.

9. Which among the following systems is used for water in high temperature range?
a) Vapor dominated systems
b) Flashed steam system
c) Liquid dominated total flow concept
d) Petro thermal systems

Explanation: Flashed steam system is used for water in the higher temperature range. Flash steam is low-pressure steam created when hot water is released from a high pressure to a lower pressure within a steam system.

10. Which geothermal systems are composed of hot dry rock (HDR) but no underground water?
a) Hybrid geothermal Fossil system
b) Flashed steam system
c) Liquid dominated total flow concept
d) Petro thermal systems

Explanation: Petro thermal systems are composed of hot dry rock (HDR) but no underground water. They are largest geothermal resource available. The rock occurring at moderate depths has very low permeability and needs to be increasing its heat transfer surface.

11. Which geothermal system utilizes relatively low temperature heat of geothermal sources?
a) Hybrid geothermal Fossil system
b) Flashed steam system
c) Liquid dominated total flow concept
d) Petro thermal systems

Explanation: The hybrid geothermal fossil fuel systems utilizes the relatively low temperature heat of geothermal sources in the low temperature end of a conventional cycle and the high temperature heat from fossil fuel combustion in the high temperature cycle with a natural source of heat for part of heat addition, thus reducing the consumption if the expensive and non renewable fossil fuels.

12. How many possible arrangements are there for Hybrid geothermal plants?
a) 2
b) 3
c) 4
d) 5

Explanation: There are two possible arrangements for hybrid plants. These are (1) geothermal preheat suitable for low temperature liquid dominated systems, and (2) fossil superheat, suitable for vapor dominated and high temperature liquid dominated systems.

Sanfoundry Global Education & Learning Series – Energy Engineering.

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