Payback calculations can be performed by evaluating the savings associated with a boiler system upgrade (incorporating the thermal efficiency gains, radiant heat loss decreasing, and electrical consumption decreasing). A payback calculation can show how long new equipment will take to pay for itself, meaning the money that would have been used to operate an old system would be used toward the cost of purchasing a new system. Simple payback is calculated as the cost of installation / yearly savings.
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
Any boiler where the products of combustion flow on the outside of a tube with the heat transfer media on the inside.
A hybrid boiler system is the one which combines the features of fire tube and water tube boilers. Depending upon the design requirements, 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 over the combustion are to absorb radiation heat and the fire tube zone absorbs the heat through convection
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 turndown ratio of 5:1 (400 divided by 80 is 5).
Modulation is the ability of a boiler to adjust its firing rate based on the temperature set point the boiler is trying to achieve. Fulton 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 Fulton Pulse 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.
A thermal fluid system is a closed loop using mineral or synthetic oil as the heat transfer fluid. These systems operate at elevated temperatures while maintaining low system pressures. Fluid is circulated within the heater tubes and flue gases heat the fluid.
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.
Presently, it is not mandatory to have an IBR operator for thermal fluid heaters.
Q: When would I use steam versus hot water or thermal fluid?
Steam carries about 540 Kcal/kg 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.
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 requirement that needs temperatures at 150°C will require steam delivered at 6 Kg/cm2 or higher.
HOT WATER SYSTEMS
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.
THERMAL FLUID SYSTEMS
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.
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.
The required operating temperature along with the physical properties (specific heat, maximum operating temperature, vapour 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.
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.
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.
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.
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.
A nitrogen blanket is required under the following conditions:
Typical thermal fluid systems are designed to operate above the fluid’s flash point and fire point but not above its auto ignition temperature.
Typically, thermal fluid will last between 5 and 8 years. Annual testing of the fluid is recommended.