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Måling af dioxinemissionen fra udvalgte sekundære kilder

Summary and conclusions

This report presents the results from a new investigation of emission of dioxin and furans from smaller combustion plants. Most of the results are from measurements initiated by this project, and they are supplemented by results from other recent measurements on similar plants.

The larger straw and wood fired plants represent the better part of the Danish plants in relation to flue gas cleaning for particles. As a substantial part of the dioxins and furans will normally be found on the particle phase, an adjusted emission factor has been calculated in relation to a higher emission of particles, up to the emission level value of 40 mg/m³(n,t,10%O₂).

Straw:

Larger plants with a good continuous combustion, a high combustion temperature, and efficient flue gas cleaning.

Measured emission.

Adjusted emission in relation to a higher emission of particles.

Small farm-size boiler, with discontinuous combustion and no flue gas cleaning.

The emission factors are considered to be representative for the majority of the straw fired plants in Denmark.

Wood and chipboard:

Bigger plants with a good continuous combustion, a high combustion temperature, and efficient flue gas cleaning.

Measured emission.

Adjusted emission in relation to a higher emission of particles.

Small semiautomatic stoker boilers, with continuous combustion, lower combustion temperature and no flue gas cleaning.

Wood stove, with discontinuous combustion, manual control and no flue gas cleaning.

The results from the stoker boiler and the wood stove show a close compliance with the figures given in the Danish investigation "Miljøprojekt nr. 249 from 1994⁴."

The emission factors are considered to be representative for the majority of the wood and particleboard fired plants in Denmark.

Barbecue:

From the oxygen concentration in the dilution channel the concentration can be calculated to be between 0.5 and 1 ng I-TEQ/m³(s,d,10% O₂). The actual concentration is considered to be much lower, due to the rapid mixing of the flue gas from the barbecue with large quantities of air. In the dilution channel, where the temperature was 39 to 56 °C, the concentrations were between 0.02 and 0.05 ng I-TEQ/m³(s,d).

Waste oil:

Unrefined waste oil in a district heating station.

This determination has a high degree of uncertainty, due to very different results for the four samples.

Refined waste oil in 2 district heating stations:

By normal operation in the 2 well adjusted plant.

By abnormal operation, poor combustion and increased soot emission in one of the plants.

The last figure is only based on one sample taken over 2 hours instead of the normal 6 hours, and the high value can be due to mistakes in sampling or analysis. But if the figure is correct, it indicates that there might be an exponential increase in emission of dioxin, if a fuel that normally gives low emission is burned under poor conditions with increased soot emission.

Crematories:

Measuring on 3 crematory furnaces in 2 crematories.

An average of all samples weighted after the number of cremations in each sample, gives an Emission factor of 350 ng I-TEQ/cremation, and a concentration of 0.3 ng I-TEQ/m³(s,d,10%O₂).

Congener pattern and I-TEQ percents:

Congener pattern and I-TEQ percents for all the samples is shown.

A congener pattern is a graphic view of the concentration or amount of each single or group of the 17 congeners normally analysed.

The I-TEQ percent is the weight of the 17 congeners in I-TEQ units, in percent of the weight before the conversion.

The congener pattern and the I-TEQ percents for each type of plant and fuel, shows a high degree of compliance, within the same fuel and combustion condition, independent of the type of plant. It has been shown, that the congener pattern and the I-TEQ percents change significantly with changes in the combustion conditions in the same plant. It shows that the congener pattern and the I-TEQ percents can be used as a simple and effective quality control of the conducted measuring. The control can be performed either on two samples from the same measuring against each other, or to control new samples against earlier samples from the same plant.

The pattern and the I-TEQ percents from two samples from the same measuring should show a very high degree of coincidence and be in compliance with earlier measurements. The I-TEQ percents may be considered as a control weighted after the TEF factors. A large deviation on a single congener with a low TEF factor will have a heavy effect on the congener pattern but a very low effect on the I-TEQ percent.

The I-TEQ percent can be used as a first and quick control of the samples to see if it is in accordance with the normal value and level for the particular plant, or the type of plant and fuel. Repeated measuring on a plant will give experience with the variation range of the I-TEQ percent.

If the I-TEQ percent deviates from the normal range it indicates incorrect results, and further investigation of the congener pattern should be performed. There may be a failure on the sampling or analysis, the operation of the plant deviate from the normal, or the fuel could be differ from normal.

In the spring 2001 the Danish EPA Reference Laboratory for Measurement of Emissions to the Air, will start to establish a database for dioxin emission measuring in Denmark. The database will be designed mainly to register data from Danish incinerators, but with the possibility to expand it to include other sources and other substances. The database will be designed to contain congener pattern and I-TEQ percents so that the theory about quality control with the pattern and percents can be evaluated with a great number of data.