WATERTUBE BOILERS AND ANCILLARY EQUIPMENT FOR MOST INDUSTRIES AND FUEL TYPES
WATERTUBE BOILERS AND ANCILLARY EQUIPMENT FOR MOST INDUSTRIES AND FUEL TYPES
Whatever your requirements are for an industrial watertube boiler, John Thompson can tailor-design a solution for you.
Irrespective of the industry you serve – from food and beverage, to sugar, pulp and paper, chemical, petrochemical, iron and steel, mining, marine or textiles, we can design, build, install and maintain a cost-effective watertube boiler for the task. With a reputation for reliability and proven performance built right in, John Thompson’s watertube boilers are available in a wide range of capacities and configurations, to suit a variety of fuels and applications. Our service offering includes site installation and commissioning, repair and maintenance, equipment retrofits, capacity and efficiency improvements, operational audits, reliability studies, metallurgical survey and remnant life analysis, operator training and the supply of OEM spares.
Whether you require a boiler that’s mono- or bi-drum, single- or multi-pass, top-, bottom- or girth supported, we can offer you designs up to 350 t/h capacity and 110 bar(g), 540 °C steam conditions.
The range includes:
Gas fired boilers
Coal-fired boilers with travelling grates and CAD spreader stokers
Biomass-fired boilers with CAD spreader stokers, pinhole grates, dump grates and vibrating grates, and
Waste heat recovery boilers
Continuous Ash Discharge Stoker
John Thompson continuous ash discharge (CAD) stokers are often installed in coal fired industrial boilers, particularly when there is a requirement for a fast response to load swings. The CAD stoker is also prescribed when coal has to be burned in combination with biomass such as bagasse, wood chips, bark, sunflower seed husk, cotton stalks etc.
Read about our continuous ash discharge stoker and how it solved production challenges for a customer.
John Thompson steam cleaned pinhole grates are ideal for burning relatively low-ash content biomass fuels. The grates are available in both air- and water-cooled versions.
On a new boiler installation, the floor tubes are typically water-cooled, forming an integral part of the boiler circulation system. The air-cooled version is ideally suited for retrofitting into hearth or "self-feeding" furnaces.
When a pinhole grate is retrofitted to an older boiler, the economics of the situation normally determine the installation of an air-cooled grate in which high pressure rearwall secondary air is passed through the support tubes. This economical arrangement allows for a boiler upgrade without the additional cost of rearranging the boiler pressure parts.
The grate bars are manufactured from temperature resistant cast iron and are profiled to nest closely on the support floor tubes.
Steam jet pressures are controlled to ensure that adequate cleaning is obtained, while at the same time ensuring that erosion is minimised on components that are impinged upon by the steam jets. A multiplicity of jets is employed to ensure that only a small section of the grate is cleaned at any time, thereby ensuring that rapid re-ignition of the fuel is achieved.
The John Thompson dump grate is used for burning a wide range of fibrous fuels, from wet bagasse to dry sunflower seed husks. It has also been successfully used for burning wood chips, saw dust and bark.
In common with the John Thompson pin-hole grate, this is often the technology of choice when converting old hearth or ‘self-feeding’ furnaces to spreader firing, where the brick-set boiler construction and limited available headroom obviates the use of other grate types.
The dump grate comprises rows of temperature resistant cast-iron keys mounted on carrier bars that pivot in bearing bushes mounted on the stoker frames. The keys have deep web sections to provide structural rigidity and to aid with cooling. Temperature resistant cast-iron cover castings are employed around the periphery of the grate and as protection for the bearings.
The grate is divided into a number of discreet sections corresponding with the number of fuel feeders / spreaders. During operation, each section of grate is dumped periodically via hydraulic cylinders that actuate the carrier bars and keys via mechanical linkages to remove sand and ash that has deposited on it. A trim damper fitted to each dumping section regulates the distribution of hot primary air to the underside of the grate, whilst facilitating isolation of the air flow to the particular section of the grate being dumped.
The system design is typically such that full boiler load can still be carried whilst individual sections are being dumped.
The dumped ash in the undergrate hopper is removed by water sluicing to quench any burning particles dumped with the ash.
The John Thompson vibrating grate was developed for the combustion of biomass and other low ash solid fuels with up to 50% moisture content.
Either air- or water-cooled, the grate surface is intermittently vibrated with the use of an eccentric drive and a leaf spring mounting arrangement to induce continuous movement of the fuel bed towards the ash discharge end. Based on the fuel preparation, particle size distribution, ash and moisture content, the grate can be sloped and the vibration frequency and duration adjusted to optimise the movement of the fuel and the ash disposal rate.
The air distribution across the depth of the grate is zoned into three sections with the undergrate combustion air supply to each section individually controlled to ensure complete combustion of the fuel prior to reaching the ash discharge end.
The grates are manufactured from suitable materials to accommodate hot undergrate combustion air at temperatures up to 250°C.
Based on the fuel geometry and characteristics, the grate movement can either be from the front to the rear of the furnace, such as when the fuel is introduced by means of a box ram or similar, or it can be configured to move the fuel from the rear of the furnace to the front, such as when the fuel is introduced by means of pneumatic spreaders.
Although the air-cooled vibrating grates can be horizontal, the water-cooled version in inclined towards the ash discharge end to facilitate natural circulation of the cooling water from the boiler circuit to which it is attached, whilst also enhancing its conveying capability. The movement of the grate is isolated from the water-cooled furnace walls to avoid any fatigue loading on the pressure parts.
The simple mechanical design and few moving parts of the versatile John Thompson vibrating grate ensure low maintenance requirements and high reliability.
Bagasse is essentially a gaseous fuel consisting of water and volatile constituents. That’s why bagasse is best handled by introducing it into the combustion chamber with part of the combustion air, and burning it whilst still in suspension.
To stabilise the heat release rate within the combustion chamber and reduce the amount of excess air required to complete the combustion, this system of combustion (which can be used with most fibrous fuels) requires a uniform spread of fuel across the full width and depth of the combustion chamber.
The first step is to meter the supply of bagasse in proportion to the boiler load. This is achieved with John Thompson three-drum rotary bagasse feeders. Two small inlet rolls in the feeder meter the bagasse supply whilst a third toothed drum positioned below the feeder rolls, runs at a higher peripheral speed. This tears and teases the incoming bagasse supply so that it arrives at the distributors in an ideal form for pneumatic spreading.
The feeders have a linear output in relation to rotational speed and each feeder is independently driven by AC variable speed-controlled motor, gearbox and final chain drive. Independent drives for the metering rolls and carding drum can be provided if required.
We offer three standard bagasse feeder capacities, covering most requirements.
Pneumatic Fuel Spreader
John Thompson combined coal and biomass air-glide fuel distributors were developed through extensive testing and have become the industry standard for modern spreader fired applications.
Manufactured from heat resistant stainless steel, each fuel spreader features an adjustable trajectory plate in the distributor throat, together with air-flow control to enable the required spread to be achieved on coal or biomass.
To optimise combustion efficiency when firing coal, the John Thompson grit re-firing system is prescribed.
This comprises a series of heat resistant cast-iron nozzles and pipes through which fly ash collected in hoppers downstream of the boiler generating bank is re-injected into the furnace so as to recover the energy from any un-burned carbon in the ash. This can equate to a few percentage points of efficiency gain and hence a significant reduction in coal consumption and fuel cost.
A mechanical cyclonic grit interceptor combined with a mud drum throw-out hopper is typically utilised to capture the fly ash after the generating bank, and secondary air is used as the motive force for re-injection.
This system is also suitable for dual fired boilers where it is undesirable to re-inject the fly ash from one of the fuels, such as bagasse. In this case, truncated hoppers and ash diverter flaps are utilised to ensure that only the required fly ash is re-injected in to the combustion zone.