Boilers for the paper and pulp industry
For this industry TIPO Kotlogradnja designs and manufactures: industrial steam boilers; hot water boilers; thermal oil boilers; waste heat recovery boilers; biomass boilers.
Each boiler is designed and manufactured to the required capacity, process requirements, fuel type and operating conditions of the plant.
The role of steam in pulp and paper production
The pulp and paper industry is a major consumer of process heat. In pulp production steam is used for cooking wood chips, in evaporators that concentrate spent liquor, and in bleaching and chemical preparation. On the paper machine water is removed in stages, and drying is the most energy-intensive of them; it relies mainly on steam-heated cylinders, with steam pressure usually lower in the early drying sections and higher in the later ones and adjusted through reduction valves to suit the paper grade and weight.
In kraft pulping, black liquor is burned in a recovery boiler, which supplies steam for the process and for a turbine while the pulping chemicals are recovered. Where there is no black liquor, steam is generated in boilers or in cogeneration plants fired with gas, biomass or biogas. For such duties steam boilers are considered, and waste heat recovery boilers come into question where a sufficiently hot gas stream is available.
Steam quality, regulation and reliability
Steam quality has a direct effect on drying. Wet steam carries less usable latent heat, and condensate that the siphons cannot remove floods the cylinders, reduces heat transfer and increases the risk of damage. During sudden load changes, droplets of boiler water can carry salts that form deposits and corrosion on traps, valves and cylinders. Steam dryness, pressure stability and boiler water quality, together with water treatment, are therefore process requirements, and swings in steam quality can contribute to web breaks.
In the EU, pulp and paper mills fall under Directive 2010/75/EU on industrial emissions, and the best available techniques conclusions for pulp, paper and board production were adopted by Decision 2014/687/EU. Those conclusions do not cover steam and power combustion plants other than recovery boilers, for which they refer to a separate reference document, and Directive (EU) 2015/2193 applies to medium combustion plants. As pressure equipment, the boiler is designed to EN 12952 or EN 12953 and PED 2014/68/EU; see standards and certificates. As mills run continuously, redundancy is planned: in one documented case an oil-fired and an electric boiler cover steam demand during maintenance of the main boiler.
Fuel, cogeneration and decarbonisation
Steam in paper mills comes from boilers and cogeneration plants fired with natural gas, biomass, biogas or black liquor. The best available techniques conclusions call for covering as much of the steam and power demand as possible by cogeneration, expected for new plants and major refurbishments and possibly limited in existing mills by layout; economic viability depends mainly on electricity and fuel costs. They also recommend high-efficiency steam boilers and energy recovery from biomass and residues where recycling is not possible, with biomass boilers as one option.
According to the European association Cepi, decarbonisation relies on energy-efficient technologies and fossil-free energy sources, including biogas, cogeneration, heat pumps and renewable electricity. Heat recovery from the humid dryer exhaust air, condensate recovery and reducing direct steam use through process integration also appear in the best available techniques conclusions. A documented waste-fired boiler shows that such fuel needs more durable materials, more maintenance and more advanced flue gas cleaning than conventional biomass.
What to define when selecting a boiler
Before a quotation is prepared, the investor should define the following; the general approach is described in how to choose an industrial boiler.
- Steam consumers and pressure levels: drying, cooking, evaporation, bleaching, and whether electricity is also required (cogeneration)
- Load profile: continuous operation, grade changes, peak loads and occasional stoppages
- Steam quality: dryness, need for superheat, pressure stability, condensate return and feedwater quality
- Fuel: gas, biomass, biogas, process residues, back-up fuel, and any available waste heat stream
- Redundancy and planned outages, emission limits, applicable standards and available space
Boiler types for this industry
Industrial steam boilers
Saturated or superheated steam for industrial, process and power applications. Shell and water-tube boilers for solid fuel, biomass, liquid and gaseous fuel.
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Hot water boilers
Hot water for industrial and energy systems and district heating. Shell and water-tube boilers for all common fuels.
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Thermal oil boilers
Thermal oil boilers serve process heating in industrial plants that need high and stable operating temperatures.
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Waste heat recovery boilers
A WHRB (Waste Heat Recovery Boiler) is a steam generator that uses the waste heat of exhaust gases from industrial processes to produce saturated steam.
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Biomass boilers
A biomass boiler burns wood chips, pellets, sawdust, bark or straw to produce steam, hot or warm water from a renewable fuel, with lower fuel costs and CO₂ emissions.
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Industrial steam boilers
- Pulp and paper
- steam and energy from wood biomass and production by-products
- Pulp and paper
- large steam quantities for drying and fibre processing
Hot water boilers
- Pulp and paper
- heat from biomass and process by-products
- Pulp and paper
- process heating and energy supply
Thermal oil boilers
- Pulp and paper
- drying and process treatment
Waste heat recovery boilers
- Paper industry
- waste heat for steam and process heating
Frequently asked questions
What is the difference between a shell and a water-tube steam boiler?
A shell (fire-tube) boiler has a large water content, is built to EN 12953 and suits small and medium capacities with stable operation. A water-tube boiler has a small water content, is built to EN 12952 and is used for larger capacities, higher pressures and superheated steam.
Which fuels can a TIPO Kotlogradnja steam boiler use?
Solid fuels (coal), biomass (wood chips, pellets, straw, husks), liquid and gaseous fuels (natural gas, light fuel oil, heavy fuel oil) and gas–hydrogen blends. The furnace and burners are designed for the chosen fuel.
Can a steam boiler produce superheated steam?
Yes. A superheater is fitted on request in both shell and water-tube boilers. Superheated steam is used for turbines and processes that need a higher temperature than saturated steam.
How are the capacity and pressure of a steam boiler chosen?
From the actual steam demand profile, the pressure and temperature required at the consumers, the fuel type and the operating regime. Our engineers run a thermal calculation on the investor's data and propose the type, size and configuration.
Shell or water-tube hot water boiler, which to choose?
A shell boiler (EN 12953) is the economical choice for small and medium capacities. A water-tube boiler (EN 12952) is chosen for higher outputs, higher temperatures and more demanding regimes, e.g. heating plants with large networks.
How is steam supplied while the main boiler is out for maintenance?
Continuous operation requires the back-up steam source to be defined in advance. In a documented paper mill example the back-up consists of an oil-fired boiler and an electric boiler, and planned outages of the main boiler are scheduled so that the back-up covers the steam demand. The size of the back-up depends on whether production may be reduced or stopped during that period.
Why does steam dryness matter for paper drying?
Wet steam carries less usable heat, and surplus condensate in the cylinders reduces heat transfer. Droplets of boiler water bring in salts that cause deposits and corrosion, and changes in web moisture affect strength, curl and printability. Steam dryness and boiler water quality are therefore specified as process requirements.
Can waste heat from a paper mill be used in a waste heat recovery boiler?
A waste heat recovery boiler needs a hot gas stream, for example the exhaust of a cogeneration plant; the best available techniques conclusions name steam and gas turbines as cogeneration options. Humid exhaust air from the dryer hood is at a lower temperature level, and the literature describes recovering it with heat exchangers and heat pumps. Each waste heat source is assessed individually.
Standards we design and build to
TIPO Kotlogradnja designs and manufactures boilers and complete boiler plants according to the investor's requirements, fuel type, capacity and operating regime. The process covers requirement analysis, solution proposal, offer, design, material procurement, manufacturing, erection, testing and commissioning. Whatever the complexity of the project or the market, the equipment is designed and built to European and international standards, including EN 12952, EN 12953, EN 13445, EN 13480, ASME BPVC and AD 2000, in line with the project documentation and the investor's requirements.
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