Wood and Coal Fired Thermic Fluid Heater

Description of Wood and Coal Fired Thermic Fluid Heater

A wood and coal fired thermic fluid heater is an industrial heating system that uses wood or coal as a fuel source to heat a thermal fluid. The thermal fluid, which is typically a specialized oil, is circulated through a closed loop system to transfer heat to the end application.

The UNIFIRE Thermal Heating system comprises two twin units, namely a radiation chamber and a convective chamber. When the fuel is burnt on a stationary grate, it produces radiant heat, which is then absorbed by a radiant coil. The remaining heat is transferred to the convective zone of concentric coils where it is absorbed, ensuring maximum heat utilization.

The system is designed to ensure minimal contamination and easy cleaning of the gas side heating surface. Wood fired thermic fluid heater is equipped with FD and ID fans to ensure optimal combustion with low excess air. Additionally, ash cleaning doors are provided for both chambers, making maintenance and cleaning easier. The unit is skid-mounted and refractory-lined, and is supplied in a ready-to-use condition, which reduces the time required for erection at the site.

Wood and Coal Fired Heater Working Principle & Construction

CONSTRUCTION DETAILS: The heater is constructed with two concentric helical closed pitch carbon steel coils connected to form a continuous flow passage, which is kept inside a shell assembly. The inner coil forms the combustion chamber (first pass), while the gap between the two coils and the gap between the outer coil and shell form the second and third passes, respectively. The unit is covered with a removable refractory cover mounted on the jacket.

To prevent human injury, the unit must be insulated with mineral wool and can be clad with AL to enhance its appearance. Thermal oil enters the unit through the inlet header and travels through the coils, picking up heat from the combustion products and getting heated before exiting from the outlet header.

AIR PREHEATER: The air preheater, with a two-pass gas side, is mounted separately and is equipped with a forced draft air fan. The combustion air is first passed through the air preheater, which preheats the air before entering the combustion chamber through the duct.

THERMAL OIL CIRCULATION PUMPS: One KSB thermal oil circulation pump is supplied for pumping the thermal oil through the heater. The pump is designed according to DIN standards and can operate at 2800C. Gland packing is provided as standard, but pumps with mechanical seals are an option.

DEAERATOR TANK & EXPANSION TANK: To avoid cavitation of the thermal oil pump, a deaerator tank is used to separate vapours continuously from the system. An expansion tank is used to accommodate the expansion of the thermal oil when heated. A thermal seal is used to connect the deaerator and expansion tanks, which reduces the degradation due to the oxidation tendency of the thermal oil. The line size used for the deaerator, expansion, vent and drain shall be minimum as recommended by DIN 4754.

CONTROL PANEL: The control panel includes switchgears and safety contacts for most of the field instruments. The safety contacts, digital inputs, and analog inputs are given as input to the controller. Feeders are supplied for the FD/ID fan, APH, TFH, and DA tank. The power and control panel are mounted inside a control room.

CONTROL PHILOSOPHY: The thermal oil heater operates based on the thermal oil outlet temperature, which is set in the temperature controller based on the process temperature requirement (max. 3000C). The signal from the outlet temperature controller is used to cut off the fans’ operation.

SAFETY:

Safety aspects are given a major focus in high temperature heater design. The following are the highlights:

Specifications

Advantages of Wood and Coal Fired Thermic Fluid Heater

1. OPERATION WITHOUT PRESSURE: The thermal fluid system is designed to operate within a temperature range of 100°C to 350°C without any increase in pressure. This system offers high efficiency, safety, and low cost compared to the use of steam at 320°C, which requires a pressure of over 110 bar and more complex equipment.
2. NON-CORROSIVE SYSTEM: The UNIFIRE system uses mineral oil as the heat transfer medium, which is non-corrosive and free from foreign particles. This ensures lower maintenance costs and higher reliability.
3. NO EXPLOSION RISKS: The UNIFIRE system offers low thermal inertia, a low-pressure system, and fully automatic safety trips for safe operation without any explosion risks.
4. NO BOILER REGULATION: The UNIFIRE heater is not regulated by the Indian Boiler regulations, eliminating the need for annual shutdowns.

List of Components 

MAIN UNIT: – THERMIC FLUID BOILER

Radiant Heat Exchanger: A single radiant heat exchanger is included, consisting of helical coils made from boiler quality BS-3059 ERW tubes of TATA or TI make, enclosed in a M.S. shell.

Convective Chamber: One convective chamber is included, consisting of a heat exchanger made from helical coils fabricated from boiler quality BS-3059 ERW tubes of TATA or TI make, enclosed in a M.S. shell.

Combustion Furnace: A single combustion furnace is included, consisting of fire grates made of heavy-duty Cast Iron grade 20.

Accessories:

The following accessories are included in the thermal fluid heater:

• One centrifugal type thermic fluid circulating pump directly coupled to an electric motor, mounted on a common base frame.
• One expansion tank cum deaerator tank.
• One induced draft fan of “Firetech” made with a base frame and control damper with an electric motor.
• One forced draft fan of “Firetech” made with a base frame and control damper with an electric motor.
• One air preheater to improve the efficiency of the unit.

Electricals:

One control panel without isolation switch but with necessary electric contactors, relays fuses, and temperature indicator cum controller will be provided.

Instruments, Controls and Safeties:

The following instruments, controls, and safeties are included in the thermal fluid heater:

• One pressure indicator on the thermic fluid inlet line indicating circulating pump discharge pressure.
• One pressure indicator on the thermic fluid outlet line indicating circuit resistance.
• One temperature indicator cum controller for combustion control on the thermic fluid return line temperature.
• One temperature indicator cum controller for combustion control on the thermic fluid outlet line temperature.
• One-gauge glass on the expansion tank.
• One differential pressure switch, connecting inlet and outlet lines for safety.

The thermic fluid line includes the following:

• Inlet and Outlet Nozzle of Deaerator cum Expansion Tank
• Inlet Nozzle of Expansion Tank for Topping Up
• Vent on Expansion Tank
• Overflow Nozzle on Expansion Tank
• Drain Nozzle of Deaerator Tank

Refractory Work:

The unit must be refractory lined with bricks as per our drawings. This falls under the customer’s scope.

Insulation:

Insulation of the unit is not included in our scope.

Performance Metrics

Fuel Specification:

The performance parameters and output of the boiler specified in this offer are valid only if the following fuel specification is utilized. Any deviation from this specification will impact the performance parameters.

Fuel Type: Wood/Agro Waste

1. Carbon: 39.26% 
2. Hydrogen: 4.00% 
3. Sulphur: 0.10% 
4. Nitrogen: 2.00% 
5. Oxygen: 32.5% 
6. Moisture (Max): 9.5% 
7. Mineral Matter: 12.64% 
8. GCV (Kcal/kg): 3500

Power Specification:

The performance of the boiler is dependent on the following power inputs:

1. Supply Voltage: 3 Phase, 4 Wire, 415 + 6% V and 50 + 3 Hz 4 Wire 
2. Control Voltage: 240 V, A.C., 1 Phase

Note: One phase of the control supply must be drawn from the three-phase supply line with the neutral.

Efficiency:

The efficiency of the boiler will be demonstrated according to the standard BS: 845 Part 1 – indirect method.

Application of Wood and Coal Fired Thermic Fluid Heater

Wood and coal fired thermic fluid heaters find applications in various industries, some of which are listed below:

1. Food processing industry: Coal fired thermic fluid heaters are used for applications such as frying, baking, cooking, and drying in food processing plants. They provide a reliable source of heat to ensure consistency in the food products.
2. Chemical processing industry: Wood fired thermic fluid heaters are used for heating reactors, distillation columns, and other equipment in chemical processing plants. They provide a high temperature heat source that is necessary for these processes.
3. Textile manufacturing industry: Thermic fluid heaters are used for dyeing, printing, and other processes in textile manufacturing plants. They provide a consistent source of heat to ensure uniformity in the colour and quality of the textile products.
4. Plywood and laminates industry: Wood fired fluid heaters are commonly used in plywood and laminates manufacturing plants. They provide a high temperature heat source that is necessary for the drying process, which is a critical step in the production of these products.
5. Rubber industry: Solid Fuel Fired heaters are used for vulcanization, a process that involves heating rubber to give it improved strength and elasticity. Wood and coal fired thermic fluid heaters provide the high temperature heat source that is required for this process.
6. Paper and pulp industry: Wood and Coal Fired Thermic Fluid Heater are used in the drying process of paper and pulp production. They provide a reliable and efficient source of heat to ensure the proper moisture content and quality of the final product.