A type of boiler that does not require a steam drum is called a once-through boiler or a once-through steam generator (OTSG). Unlike traditional boilers, which typically have a steam drum to separate water and steam, a once-through boiler operates without a steam drum. Instead, it directly produces steam as water passes through the boiler tubes.
In a once-through boiler, the water enters the boiler at one end and flows through a series of closely spaced tubes. These tubes are designed to withstand high pressures and temperatures. As the water flows through the tubes, it absorbs heat from the combustion gases, and its temperature rises.
Due to the high pressure and flow rate, the water quickly reaches its boiling point and undergoes rapid vaporization. As a result, the water transforms into steam within the tubes. The steam and remaining water mixture then continue to flow through the tubes until the desired steam quality is achieved.
Once-through boilers offer several advantages, such as:
Compact Size: Without the need for a steam drum, once-through boilers can be more compact and have a smaller footprint compared to traditional boilers, making them suitable for applications with limited space.
Rapid Startup: Once-through boilers can achieve steam production quickly, as they do not need to wait for the entire water volume to heat up and reach saturation temperature.
Better Response to Load Changes: Due to their design, once-through boilers are typically more responsive to changes in steam demand. They can adjust their steam production more rapidly than boilers with steam drums.
Improved Efficiency: Once-through boilers can achieve high thermal efficiencies, as they minimize heat losses associated with maintaining a large water volume in a steam drum.
Once-through boilers are commonly used in applications where a continuous supply of high-pressure steam is required, such as power plants, industrial processes, and marine propulsion systems. However, it's worth noting that the design and operating parameters of once-through boilers need to be carefully controlled to ensure safe and efficient operation.