Claes Tullin

Particle emissions from biomass combustion in small combustors

Literature data on particle emissions are compared with emissions from combustion of wood pellets and wood briquettes in commercial small-scale combustion devices: a pellet stove, two pellet burners and two smaller district heating boilers. The influence of operating parameters and fuel quality was investigated. Mass concentration, number concentration and number size distribution of particles were determined. The mass size distribution was analysed as well as the inorganic components. Gaseous compounds were recorded to give information about the combustion conditions. The mass concentrations of particles were between 34 and , increasing during unsatisfactory operation conditions. The number concentration was in the range of 107–108 particles per Ncm−3. The particle emission was dominated by submicron particles (size ), both from number and mass perspective. The main inorganic components of the submicron particles were potassium, sulphur, chlorine and oxygen. Small amounts of sodium, magnesium and zinc were also found. The contents of potassium, chlorine, and sulphur in the fuel are important for the composition of the emitted inorganic submicron particles.

Experimental Wood Smoke Exposure in Humans

Experimental studies are used to evaluate effects of human exposure to diesel exhaust and concentrated ambient particles. This article describes a system for studying exposure of humans to wood smoke. Wood smoke was generated using a wood stove placed outside an exposure chamber that can hold at least 10 subjects. A partial flow of the generated wood smoke from the stove was mixed with filtered indoor air. Personal and stationary measurements were performed of PM2.5 and PM1 mass concentrations and various volatile organic compounds (VOCs): 1,3-butadiene, benzene, and aldehydes. In addition, particulate matter (PM) mass, number concentrations, and size distributions of particles (0.007–6.7 μm), as well as nitrous oxides, CO2, and CO, were measured online. Filters were analyzed for trace elements and black smoke. Polycyclic aromatic compounds, toluene, and xylenes were determined in stationary samples. Results of the first experiment showed no differences between personal and stationary measurements for particles or VOCs. Consequently, stationary measurements can be used to predict personal exposure. All PM mass (about 250 μg/m3) was in the PM1 fraction. Subjective symptoms were generally weak, while clear objective signs were found, for example, in biomarkers of inflammation. With careful control of the combustion process, relatively constant mass and number concentrations were obtained over each exposure session. By varying the combustion and dilution of the wood smoke, different exposure scenarios can be achieved and thus, knowledge about which of the properties of particles and gaseous compounds are crucial for the effects.

The temperature's influence on the selectivity between HNCO and HCN from pyrolysis of 2,5-diketopiperazine and 2-pyridone ☆

Two cyclic amides, 2-pyridone and 2,5-diketopiperazine (DKP), were pyrolysed at temperatures ranging from 700 to 1100C. Pyridone is the only one of the four main nitrogen functionalities found in coal that is likely to form HNCO under pyrolysis. DKP is a primary pyrolysis product from proteins, which are the main nitrogen source in biomass. The formation of HNCO from biomass has been suggested to originate from DKP and other cyclic amides. The aromatic 2-pyridone was thermally more stable than the non-aromatic DKP. Both amides formed HCN, HNCO and NH3. The NH3 yields, about 3–4% for 2-pyridone and 10% for DKP, were almost independent of temperature. The HCN yield on the other hand showed strong temperature dependence and increased with temperature for both of the cyclic amides. The HNCO yield decreased with increasing temperature for DKP over the whole temperature interval. For 2-pyridone, the pyrolysis was incomplete at the lowest temperature in the investigation. Between 900 and 1100C, the pyrolysis of 2-pyridone was complete and the HNCO yield decreased with increasing temperature. The HNCO/HCN ratio for both of the cyclic amides decreased with increasing temperature over the whole investigated temperature range. The finding in literature that the HNCO formation from cracking of coal tars produced a maximum HNCO yield at an intermediate temperature, is explained by the thermal stability of pyridone at low temperatures and the selectivity towards HCN at high temperatures.

Report: waste refinery in the municipality of Borås.

This paper briefly describes waste treatment trends in Sweden and describes an example of state-of-the-art treatment in a local integrated waste treatment system (Borås). The focus is on treatment of household waste, to illustrate what can be done to establish a sustainable waste treatment system with high recovery of materials and energy. The various processes have resulted in a low amount of landfilled household waste, and high proportions of recovered energy and materials. Heat, electricity, vehicle fuel and fertilizers, metals and construction materials are recovered from the local waste in Borås, with less than 4% of domestic waste being sent to landfill.

Co-combustion of pulp and paper sludge with wood -- emissions of nitrogen, sulphur and chlorine compounds

Sludge from wastewater treatment plants in five Swedish pulp and paper mills has been burned together with wood in a circulating fluidised bed (CFB) boiler. The sludge was either mechanically dewatered or pre-dried. The mechanically dewatered sludge had to be fed with a pump, but the pre-dried sludge could be fed by the fuel feed system normally used for coal, wood chips or wood pellets. In parallel to the combustion tests in the CFB boiler the sludges were also investigated as single fuels in a small laboratory FB. The Swedish pulp and paper industry produces three major fractions of sludge: pure fibre sludge, sludge produced by employing a precipitation species like ironaluminiumsulphate, and finally, sludge subjected to biological cleaning. The way of production of the sludge influences its content of, for example, nitrogen, sulphur and chlorine, but the composition of the sludge is also influenced by the pulp and paper process. The present measurements show that the concentrations of nitrogen, sulphur and chlorine in the sludge have a great impact on the corresponding gaseous emissions from combustion. Actions to prevent these emissions could be necessary, depending on the origin of the sludge and treatment process used. In the present project all sludges were burned with wood-pellets as the main fuel under identical operating conditions, typical for a CFB boiler. Wood pellets were chosen as a well defined, low-polluting fuel that makes comparison of emissions from the sludges clear. Co-combustion with wood-pellets has the advantage of enabling operation also with wet sludges that cannot be used as single fuels without pre-drying. No actions were taken to improve sulphur and chlorine retention, by for example adding limestone. From a combustion point of view the co-combustion works well with low levels of carbon monoxide present in the flue gas and no light hydrocarbons.

Heat generation from biomass in Sweden

Sweden now has more than 50% renewables in the energy system with bioenergy as the single largest energy source providing in total about one-third of final energy use. Through a combination of efficient policies, such as the carbon dioxide tax and applied research, the heating sector has been successfully decarbonized. In addition, power production from biomass makes an important contribution to renewable power in Sweden. The major remaining challenge to decarbonize the energy system is to replace fossil fuels in the transportation sector.