In a Sunrod marine boiler a waterwall makes a gas-tight
furnace from which the flue gases pass through the Sunrod pin tube elements to
the smoke-box on the top of the boiler.
You may consider the Sunrod boiler as a hybrid between fire tube boilers and
water tube boilers. The
membrane panel consists of water tubes, but the Sunrod
element is a flue tube with a water-tube inside.
Svenska Maskinverken originally designed the Sunrod boiler but
nowadays several boilermakers manufacture them.
water and steam flow diagram
Blue: the downcomers lead the water from the steam drum to
the circular water drum.
Red and blue: the waterwalls lead the water and steam emulsion
back to the steam drum.
Note the heavy steaming in the Sunrod tubes.
Red: Steam to the consumers.
The Sunrod boiler tubes
The Sunrod boiler tubes, with the extended surface, make it possible to
provide body compactness combined with the large furnace volume.
This gives good combustion, high efficiency, low furnace load and low stress in
the furnace body material combined with very quick response in steam
The self-circulation in the boilers vertical tubes, with the gas side surface
extended by the tube-pins, is very efficient due to the high heat transfer from
the gas to the water.