Frequently Asked Questions
What is a fire tube boiler?
Fire Tube Boiler : Any boiler where the products of combustion flow on the inside of a tube with the heat transfer media (ex. water, steam, or hot oil) on the outside. The tubes can be orientated vertically, horizontally or at an angle
What is a water tube boiler?
Water tube boiler : Any boiler where the products of combustion flow on the outside of a tube with the heat transfer media on the inside.
What is a hybrid or combination boiler system?
A hybrid boiler system is the one which combines the features of fire tube boilers and water tube boilers. Depending on the design requirements, a certain percentage of the heat transfer area is the water tube portion and the rest is the fire tube.
These are generally designed for non-conventional agro-waste fuels like husk etc., which need high volume to burn efficiently. Hence a water tube portion is provided by the combustion are to absorb radiation heat and the fire tube zone absorbs the heat through convection
What is the turndown of a boiler?
Boiler Turndown is the ratio of a boiler’s minimum fuel input as compared to its maximum fuel input.
For example, a boiler with a maximum fuel input of 400 Kg/hr and a minimum fuel input of 80 Kg/hr would have a turndown ratio of 5:1 (400 divided by 80 is 5).
What is modulation?
Boiler Modulation is the ability of a boiler to adjust its firing rate based on the temperature set point the boiler is trying to achieve.
Boilers can be built in a number of electrical configurations to accomplish modulation by operating off the controls on the boiler itself or receiving a signal from a control system or building management system.
For example, a boiler with a maximum fuel input of 2,000,000 Btu/hr, would be set up to operate and any input between 400,000 Btu/hr and 2,000,000 Btu/hr.
What is a thermal fluid system?
A thermal fluid system is a closed loop using mineral or synthetic oil as the heat transfer fluid. Thermal fluid systems operate at elevated temperatures while maintaining low system pressures. Fluid is circulated within the heater tubes and flue gases heat the fluid.
When should I use a thermal fluid system?
The choice between a steam system or a thermal fluid system is governed by the process requirements.
The range or process temperature is a deciding factor. If the system’s required temperature is above the freezing point of water (0°C) and below approximately 160°C, the choice is usually steam.
However, if the required temperature is above 160°C, thermal fluid may be a better solution.
Thermal fluid heater systems can be designed with maximum operating temperatures to 325°C.
Is a qualified Boiler operator required for thermal fluid heaters?
Presently, it is not mandatory to have an IBR operator for thermal fluid heaters.
When would I use steam versus hot water or thermal fluid?
Steam carries about 540 Kcal/kg of useful energy whereas hot water and thermal fluid carry much less energy. Steam does not require a pump to transfer the energy. Generally, if the heating temperatures required are <100°C, then hot water can be used and if temperatures >180°C are needed then thermal fluid might be a better choice. For process temperatures between 100°C and 180°C steam is considered a viable option.
When should I use high-pressure versus low-pressure steam?
The pressure of the steam is directly related to its temperature. So process temperature will require steam used to be at a specified pressure. For example, a process requires that needs temperatures at 150°C will require steam delivered at 6 Kg/cm2 or higher.
Why do boilers have a minimum flow requirement?
Boilers with low water volumes require a minimum flow requirement to prevent localized boiling and subsequent heat exchanger damage in a low to zero water flow situation. Minimum flow requirement varies by boiler design. Regardless if a boiler itself has a minimum flow requirement, every hydronic heating system needs to be designed to carry the energy being created away from the boiler to avoid high temperature shut down.
Is there a minimum flow requirement for a thermal fluid heater?
A minimum flow rate is required in order to maintain the appropriate velocities through the heater (typically 3 – 4 m/sec). If the velocity is too low the film temperature could increase, potentially destroying the fluid.
What are the primary components of a thermal fluid system?
A typical system includes the heater, circulation pump, expansion tank, and the user’s process. Depending on the temperature requirements and the system design control valves may also be utilized.
How do I choose a thermal fluid?
The required operating temperature along with the physical properties (specific heat, maximum operating temperature, vapor pressure, specific gravity and coefficient of thermal expansion) of the fluid should be evaluated when choosing a thermal fluid. It is important to choose a fluid specifically designed for heat transfer.
Can thermal fluids be mixed?
Mixing different fluids and subjecting them to high temperatures can have unpredictable results. In addition, once fluids have been mixed, the baseline analysis of the fluid is no longer applicable making it difficult to perform an annual analysis of the fluid for degradation.
Why is an expansion tank required?
All thermal fluids expand as they are heated. The amount of expansion is based on the operating temperature, system volume and the coefficient of thermal expansion of the fluid. An expansion tank must be provided to accommodate the increased system volume at operating temperature. NOTE: All fluids expand at a different rate.
What types of materials (valves, piping, gaskets etc.) should be used with thermal fluid systems?
Typically, thermal fluid systems should use either carbon or stainless steel components. Brass, bronze, cast iron, and aluminum are incompatible with thermal fluid. Piping should preferably be schedule 40 seamless SA 106 material. Valves should be cast steel with stainless steel trim. Gaskets should be rated for the temperature and pressure of the system. NOTE: Threaded connections larger than 1” should not be used in the flow circuit.
What is a nitrogen blanket?
When an expansion tank is pressurized with nitrogen (to eliminate the possibility of exposure of the fluid to oxygen), it is said to have a nitrogen blanket.
When is a nitrogen blanket required?
Can I operate the system above the thermal fluid’s flash point?
Typical thermal fluid systems are designed to operate above the fluid’s flash point and fire point but not above its autoignition temperature.
What is the lifespan of thermal fluid.
Typically, thermal fluid will last between 5 and 8 years. Annual testing of the fluid is recommended.