Benson Boiler: Know Diagram, Construction, Working, Advantages and Applications

Benson boiler is a high-pressure, water tube steam boiler known for its ability to generate superheated steam efficiently. Invented by the German engineer and visionary Mark Benson in the early 20th century, this innovative boiler design revolutionised steam generation efficiency, safety, and performance in power plants and industrial processes. The Benson boiler's distinctive feature lies in its ability to operate at supercritical pressures, surpassing the limitations of traditional boilers.

This blog will focus on Benson Boiler, its working principle, components, advantages and disadvantages. This topic in mechanical engineering is important for your upcoming examinations like SSC JE ME and RRB JE Mechanical Engineering.

What is Benson Boiler?

The Benson boiler is a high-pressure, drumless water tube steam boiler that operates through forced circulation. It distinguishes itself by introducing feed water at one end and expelling superheated steam at the opposite end. Achieving supercritical pressure (exceeding the critical threshold of 225 bar), the feed pump facilitates the direct transformation of water into steam without the need for boiling. Benson boiler is one of the high-pressure boilers having the unique feature of producing steam at supercritical pressure, which means it operates at a pressure and temperature above the critical point of water, resulting in improved thermodynamic efficiency and power generation capabilities.

Working Principle of Benson Boiler

Fig 1: Benson Boiler

The diagram illustrates the Benson boiler, a water tube boiler operating on the principle of water's critical pressure, denoting the point where water and gas states are in equilibrium.

In the Benson Boiler, the feedwater flows through the economizer to the furnace's water-cooled walls, absorbing heat through radiation, thereby raising its temperature close to the critical level. Subsequently, it enters the evaporator, potentially undergoing superheating. Finally, the feedwater is directed through the superheater to attain the desired level of superheated steam.

This particular boiler, often referred to as a lightweight boiler, lacks a sizable water and steam drum. It can achieve an impressive thermal efficiency of up to 90%. Typically operating at an average pressure of 250 bar and a capacity of 135 tons per hour, this boiler can be ready for use in just 15 minutes.

Benson Boiler consists of the following Main Parts:

• Chamber
• Water Feed Pump
• Blower
• Furnace
• Economizer
• Air Preheater
• Radiant Superheater
• Convection Evaporator
• Convecting Superheater
• Throttle Valve
• Chimney

Feed Pump:

The Benson boiler employs forced water circulation, and a feed pump is instrumental in delivering water to the boiler at critical pressure.

Air Preheater:

Before entering the combustion chamber, air undergoes preheating, which significantly enhances the boiler's efficiency.

Economizer:

Water sourced from the feed pump initially traverses through the economizer. Here, combustion gases are harnessed to preheat the water, contributing to the boiler's overall efficiency.

Radiant Evaporator:

Subsequently, the water from the economizer proceeds to the radiant evaporator, where heat transfer occurs through radiant methods. This section is situated in close proximity to the combustion chamber.

Convective Evaporator:

Within the convective evaporator section, convection is the mechanism through which heat is transferred from flue gases to the water, leading to complete water evaporation.

Convective Superheater:

The convective superheater serves as the final chamber in the boiler. Steam flows through this chamber, elevating the steam's temperature. The resulting superheated steam is then extracted for industrial processes.

Fig 2: Parts of Benson Boiler

Features of Benson Boiler

The primary challenge encountered in La Mont boilers is the formation and adhesion of bubbles on the inner surfaces of heating tubes, impeding heat transfer and steam generation due to their higher thermal resistance compared to the water film. However, several advantages distinguish Benson boilers:

(a) Elevating the boiler pressure to the critical level (225 atm) eliminates the risk of bubble formation as steam and water attain the same density.

(b) Unlike natural circulation boilers, Benson boilers do not necessitate expansion joints because of welded pipes, simplifying erection and saving time.

(c) Transportation of Benson boiler components is hassle-free as it lacks drums, allowing most parts to be transported without pre-assembly.

(d) Benson boilers can be installed in relatively compact spaces, with size not constrained by space limitations.

(e) The use of small-diameter, closely spaced tubes enhances furnace wall protection in Benson boilers.

(f) The Benson boiler incorporates the superheater into the forced circulation system, eliminating the need for special starting arrangements.

(g) Quick starts are possible in Benson boilers due to welded joints.

(h) Benson boilers can be operated with optimal efficiency by adjusting temperature and pressure at partial loads and overloads while maintaining desired temperature levels.

(i) Benson boilers exhibit insensitivity to load fluctuations, making them ideal for grid power 

stations as they can adapt to sudden load changes effectively.

(j) Blow-down losses in Benson boilers are minimal, accounting for only 4% of boilers with similar capacity using natural circulation.

(k) Explosion hazards are considerably lower in Benson boilers, as they consist mainly of small-diameter tubes and possess limited storage capacity. During startup, water passes through the economizer, evaporator, superheater, and back to the feed line via a starting valve. To prevent overheating of evaporator and superheater tubes, the circulating pumps start before the burners during the startup process.

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Benson Boiler vs LaMont Boiler: A Detailed Comparison

Both Benson and LaMont boilers are high-pressure water tube boilers commonly used in thermal power plants. Benson boiler operates on the principle of critical pressure, while Lamont boiler uses a steam drum and a circulation pump to maintain water flow through tubes. Benson boilers are ideal for modern, large-scale power generation systems.

Feature	Benson Boiler	LaMont Boiler
Pressure Range	Supercritical	Subcritical
Steam Drum	Not Required	Required
Circulation Method	Natural (forced once-through)	Forced with a circulating pump
Efficiency	Higher due to no latent heat losses	Lower compared to Benson
Startup Time	Faster	Slower
Construction Complexity	Simpler	More Complex (pump + drum)
Suitability	Large-scale power plants	Medium-pressure industrial plants

Advantages of Benson Boilers

The various advantages of Benson Boilers are:

• The absence of a water-steam separator drum in the Benson boiler reduces overall boiler costs.
• The Benson boiler boasts portability, enabling convenient transportation between stations.
• It combines cost-efficiency with enhanced performance, making it an economically attractive choice.
• It accommodates pressures exceeding 350 bar without changing the evaporator.
• The quick and seamless startup enables the boiler to reach its maximum load capacity in just 10 minutes.

Disadvantages of Benson Boilers

Some of the conspicuous disadvantages of this boiler are:

• Excessive tube temperatures can lead to inadequate water supply.
• Given its limited storage capacity, precise synchronisation among steam, feedwater, and feed inlet is imperative.
• If impure water is present, the evaporation process can carry salts and solids into the tubes, potentially resulting in significant damage and blockages.
• Managing the boiler for varying loads can pose challenges and complications.
• Continuous inspection is essential to avert the risk of explosions, which may occur due to the supercritical pressure present.

Applications of Benson Boilers

The application of Benson boilers include:

• Benson boilers are extensively used in modern power plants for efficient steam generation.
• They find application in both fossil fuel-fired and nuclear power plants.
• They are employed in combined cycle power plants to maximise energy conversion.
• They play a vital role in industrial processes requiring high-pressure and supercritical steam.
• Benson boilers are utilised in thermal desalination plants to produce fresh water from seawater.
• They are employed in cogeneration systems for simultaneous heat and power generation.

Why is Benson Boiler Used in Modern Power Plants?

Benson boilers are widely used in modern power plants due to their efficient design and ability to operate at high pressure. It operates adobe the critical pressure of water where the distinction between water and stream disappears. This results in faster head transfer, faster stream generation and thermal efficiency. The biggest advantage of the Benson boiler is its rapid startup ability. It can reach the full load conditions in a short period of time, making it ideal for power plants. Benson boilers eliminate the risk of bubble formation in water tubes, which can lead to uneven heating and tube failure. These features make the Benson boiler well-suited for large-scale thermal power plants that require high-capacity power generation. 

This elaborate article sailed readers through the details pertaining to Benson Boiler. We recommend our readers they should appear in the SSC JE Mechanical mock tests and SSC JE ME Previous Years Papers. Also, get enrolled in the AE/JE Mechanical coaching to get a firm grip on the subject.

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