Water Tube Boiler – High-Efficiency Steam Generation for Industrial Applications

A high steam output ( up to 500 TPH)

INTRODUCTION

Water Tube Boiler

Boilers are amazing machines designed to convert chemical energy in fuel into heat energy for production.

Currently, boilers are researched and developed into many types for application in many different cases. Classification of boilers can be based on structural characteristics or characteristics of the fuel source that the boiler uses, such as solid fuel-fired boilers, and gas-liquid fuel boilers.

General description of water tube boiler system

Water tube boilers have a capacity range from 5 – 550 TPH. This is a very wide capacity range, covering almost all types of boilers currently on the market. Furthermore, the pressure and temperature ranges are equally wide, reaching up to 165 bar and 540oC.

Therefore, theoretically, liquid-gas-fired water-tube boilers can meet a variety of uses related to thermal energy.

Regarding fuel, the origin and characteristics of petroleum fuel are quite diverse, for example: DO oil, FO oil, R-FO oil, KO oil; gases such as LPG, CNG, blast furnace gas (BFG), coke oven gas (COG), Off-gas, etc.

Each type of oil and gas has different physical and chemical characteristics, leading to different burner selections for them. However, these fuels still have many similarities. Therefore, the structure of this furnace system can be used for many types of liquid-gaseous fuels. Even in many cases, the furnace system is designed to burn these fuels at the same time.

Water Tube Boiler

Pictures of some gas-oil burners

Equipment in the oil-gas water tube boiler system

In general, the equipment in the oil-gas boiler system tends to be simpler and more compact than the solid fuel boiler with the same capacity.

Below is the necessary equipment for an oil and gas boiler system to work properly.

– Fuel feed system: There is a difference between the feeding system for gas fuel and liquid fuel. Typically, gas-fired furnaces have an additional device that controls and measures pressure and temperature called a gas train. As for the liquid fuel-fired boiler, a booster pump system must be installed.

– Burner: The burner is one of the most important devices in the furnace system. Here, the air and fuel are mixed, and burned, creating thermal energy to supply the system.

– FD and ID fan system: For boilers with small capacity, the fan is usually designed with a burner, so the air supply system is very compact. In contrast, in large-capacity boilers, the fan is often designed separately from the burner, and sometimes, a smoke recirculation system is also designed to increase furnace efficiency and better control NOx.

– Heat recovery system: A conventional Heat recovery system includes an economizer and an air preheater. Because the hot smoke coming out of the boiler often has a high temperature, if it is discharged directly into the environment, it will cause a waste of energy. Therefore, to save energy, manufacturers will design more economizers (installed at the location where smoke exits the furnace) to recover this energy, thereby improving the efficiency of the boiler system. These economizers are usually made of finned tubes because the exhaust fumes from oil-gas fired boilers are usually very clean, and not afraid of dust.

– Furnace: A water tube boiler with a combustion chamber is composed of boiler wet walls, water is inside the tube, the fuel burned in the combustion chamber will transfer heat to the water inside the tube, and after burning, the smoke is hot. will pass through the steam generator beams to continue to exchange heat and escape to the outside of the boiler.

– Exhaust gas treatment system: Mostly used in the case of FO/R-FO combustion, people often have to install an additional SO2 absorption tower to remove this gas before releasing the smoke into the atmosphere.

– Water tank system and water supply pump for the boiler: To ensure a stable water supply for the boiler system, it is often necessary to design a large enough volume water tank (usually designed according to HEI standards). Also based on the consideration of the stable operation of the system, today’s water pumps are often equipped with an inverter that can change the flow of water supplied to the furnace when the demand for steam changes.

– Measurement and control system: The control of combustion and feed is integrated into most of the controllers pre-programmed by the burner manufacturer.

Classification & Principles of Operation

A-shaped furnace is a type of boiler with one steam boiler and two water boilers. The burner position is located in the center of the furnace. Connecting the steam drum together is a system of pipes located around the burner.

Closer to the burner, the duct will be exposed to a high heat source, thus generating more steam. Therefore, pipes located near the burner will draw water from the water drum and release the steam (and the water that has not yet evaporated) into the Steam drum.

In contrast, the pipes located close to the outer wall of the boiler, far from the burner, exposed to a lower heat source will lead water from the steam drum to the water drum.

Water after returning to the water drum continues to start a new cycle until it becomes steam in the Steam Drum. Here, the steam is separated and directed to the superheater (if any) to the point of consumption.

A-shaped Water-tube boiler

As for the smoke, after radiating heat at the combustion chamber and out of the combustion chamber, it will be divided into two equal parts and enter 2 convection passes distributed on both sides of the furnace. After going through the convection pass, they will be collected before going to the heater or going straight to the chimney.

D-shaped Boiler

The D-shaped boiler consists of a steam boiler located on the top and a water drum below. Because the layout is different from the A-shaped boiler, the path of the pipeline is also different.

Instead of going from 2 directions like the A-shaped boiler, in the D-shaped furnace, the smoke will go all into 1 pass (convection pass) and then out of the furnace at the opposite end of the pass.

Water Tube Boiler

D-shaped Water-tube boiler

O-shaped Boiler

The operating principle of the O-boiler will be completely similar to that of the A-boiler. The difference is that the O-shaped furnace has only one water drum, so the pipeline will rotate around the burner and connect the water drum to the steam drum.

Water Tube Boiler