Services | Projects | Co-operation partners | News | Contact us  
Waste-to-energy Technology

Technology description

In pyrolysis, large hydrocarbon molecules (cellulose, hemicelluloses and part of the lignin) break down into smaller and lighter molecules. Unlike combustion and gasification, pyrolysis occurs in total absence of oxygen. Oxygen can be added to the pyrolysis chamber, when some combustion is allowed to produce heat for the process. (Basu 2010)

The initial steps of conventional pyrolysis are usually drying and milling. From milling, raw material enters the pyrolysis chamber, where temperature is high. Condensable volatile gases (heavy hydrocarbons) are recovered and condensed after separation step. Solid products (charcoal) and liquid tar are separated for further treatment and utilization. (Basu 2010)

Pyrolysis can be divided to slow and fast pyrolysis. In slow pyrolysis, biomass is heated slowly to pyrolysis temperature (400-800 °C) with long residence time. Slow pyrolysis produces more tar and charcoal and less gases. The purpose of fast pyrolysis is to maximize the yield of liquid or gases. In fast pyrolysis, biomass is heated rapidly to the adequate temperature (up to 650°C), and held there only for few seconds or less than second. Also flash and ultra-rapid pyrolysis has been researched. Known reactor types are fixed bed, moving bed, bubbling fluidized bed and circulating fluidized bed reactors. (Basu 2010, EUBIA 2011)

Condensable pyrolysis gases can be condensed into bio-oil, which can be utilized for vehicles or in CHP-units. Other lighter gases (CO2, CO, CH4) can be combusted and thus heat can be produced. Tar from the process can be also treated to improve bio-oil yield. Solid residues, especially charcoal, can be sold or utilized in heat production or barbeques. (Basu 2010)

Installation of a pyrolysis plant

Installation of a pyrolysis plant starts with determining the amounts and properties of feedstock, so the circumstances, catalysts, reactor size etc. can be considered. Also it is good to define desired end product, which can be gas, charcoal or bio-oil, so operating temperatures, residence time, product yield and heating rate can be thought out. In addition, raw material suppliers are essential to find and make agreements with them. (Basu 2010)   

After determination of raw materials, construction permit is needed to the plant. Land use can also be regulated, and it is possible to consider the city plan to find an appropriate location for the pyrolysis plant. Properties of pipes and storages are regulated and their installation of them may need permission. Installation of liquid and gas devices is done by following appropriate requirements. (Ministry of Environment 2011a)
Environmental permit for the pyrolysis plant is compulsory, due to its potential environmental hazards. Environmental Impact Assessment is necessary to compose, and regulations and legislative systems related to waste streams are taken into account. In addition, it is possible to consider also the IPPC Directive, but the need of this directive varies from country to country and can depend on the size of the pyrolysis plant. Also the collection and transportation of waste is regulated by the EU. These regulations vary also from country to country. (Ministry of Environment 2011a)  

Safety issues are one of the fundamentals of the pyrolysis plant because of several fire and explosion hazards. Hazard identification, risk assessment and possible rescue plan is thus necessary to compose. In small-scale applications, at least a notification to the local rescue authority is compulsory. Regulations regarding electrical and pressure equipment and machinery are necessary to follow. Adequate handling, transportation and storing of several hazardous substances is essential to avoid accidents. (Ministry of Environment 2011a, Basu 2010)     

Selling bio-oil, heat, electricity and charcoal from the pyrolysis plant requires agreement with companies. Possible buyers and markets are taken into consideration in an early stage of the planning process. (Ministry of Environment 2011a) 
Legislative systems and requirements can have national and regional differences. To avoid major problems with legislative systems and regulations, discussions with local authorities at an early stage of the gasification plant planning process is a necessity.

Pyrolysis safety issues

The pyrolysis process is producing and handling hazardous compounds, such ase CO, H2 and hydrocarbons. Carbon monoxide is very toxic compound; it can cause dizziness and even in low. For the possible leaks of CO, a ventilation system and a CO detection device are necessary. Furthermore, glowing particles can ignite or cause an explosion, if there is a source for ignition present. (Gasification guide 2009)

Hydrogen can also be a source of safety hazard in the pyrolysis plant. For humans, hydrogen is an undetectable compound, so it can be detected only by special device. At high concentrations, hydrogen can ignite very easily, causing fires and explosions. Also hydrocarbons can cause fire and explosion hazard, if there is source for ignition. Transportation and storage of CO, hydrocarbons and H2 is hence necessary to do following adequate requirements and standards. The ATEX Directive is to be considered at very early stage of design. (DOE 2006) (Basu 2010) 

Fluctuating and too high pressure can cause damage to process equipment and lead to leaks and malfunctions. High temperature can lead to hot surfaces and thermal shock. Occupational safety issues have to be considered also during risk assessment. Occupation hazards include, among others, hot surfaces, noise emissions and electrical, machinery and exhaust gas hazards. Electrical hazards can lead to static electricity build up and sparks, causing an explosion in the worst case. (Basu 2010, Gasification guide 2009)

Malfunction in the process, for example electrical malfunction, or inadequate activity of boiler can cause hazards. In addition, boiler feed-water and steam loss can cause boiler malfunctions. Electrical malfunction can cause problems with control systems, with severe consequences. Finally, the bio-oil and charcoal have be stored, handled and transported properly to prevent any safety and health hazards. (Basu 2010)


Pyrolysis temperature, heating rate and residence time together affect significantly to product yield. The context between these parameters and those effecting on product yield is presented as follows:

  • Slow heating rate (< 0,01- 2,0 °C/s), low temperature and long residence time maximize the production of char
  • High heating rate, intermediate temperature (450-600 °C) and short gas residence time maximize the liquid yield
  • Slow heating rate, high final temperature (700-900 °C) and long gas residence time maximize the gas yield.

Gas production can be controlled mostly by temperature. CO2 yield is high at low temperatures, and decreases when temperature increases. Hydrogen production increases, when temperature increases. (Basu 2010)


Basu Prabir (2010) Biomass Gasification and Pyrolysis. Elsevier Science Publishing Co Inc . 376 p. ISBN: 978-0-12-374988-8

Chartier P, Ferrero G.L, Henius U.M, Hultberg S, Sachau J, Wiinblad M (1996) Biomass for energy and environment. Volume 2. Copenhagen, Denmark. 1473 p. ISBN: 008-0428495

European Biomass Industry Association (EUBIA) 2011. [Internet pages]. [Cited 13 June 2011]. Available at:

Gasification guide 2009. Guideline for Safe and Eco-friendly Biomass Gasification. European Commission 2009. Available at:

Ministry of Environment 2011a. Environmental permits [Internet pages]. [Cited 26 June 2011]. Available at: =




Project homepage

Contact person:
Eva Pongrácz

Previous page