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Characterisation of Stormwater in Biomass Combined Heat and Power Plants Modelling and Experimental Investigation
KTH, School of Chemical Science and Engineering (CHE).
2014 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Water shortage in several places on this planet together with an increasing environmental awareness have recently been

inciting a growing need in society for infrastructural investments giving stormwater, originating from rainfall or snowmelt,

priority as an important water resource assets. Even though polluted stormwater usually is extensively accounted for on

multiple levels in urban planning, this is usually not reflected in the operational standards on many industrial sites. Biomass

combined heat and power (bio-CHP) plants, incorporating large biomass storage facilities outdoors, have a potential of

discharging pollutants through stormwater run-off. In order to adequately manage this somewhat diffuse source of pollutants,

a proper understanding of the parameters governing stormwater formation and composition, together with proper tools to

model this on a continuous basis, are needed.

With the aims of increasing the industry-wide capability to monitor the quantity and quality of stormwater discharged from

bio-CHP plants, a series of field experiments were conducted at Idbäcken bio-CHP, a Vattenfall owned facility, in Nyköping

(April-June 2014). The experimental work involved measuring of run-off routing on plant in connection with rainfall as well

as analysis of different water quality indicators in samples collected in a local drainage ditch. Additionally, a rain simulator

was used to investigate quality, magnitude and dynamics of discharge aspects of biomass leaching, under controlled

conditions. The results from these experiments were analysed together with local meteorological data resulting in an annual

mass balance for the pollutants. An iterative multiple regression analysis was also made in Excel producing a statistically

significant linear relationship between run-off volumetric load (m

3), 􀜸􀜴􀜱 , precipitation intensity (mm), P, and amount of

biomass stored (m

3), 􀜸􀜤􀜫􀜱 , (Equation I).

􀜸

􀜴􀜱 = 3.9􀜲 􀵆 0.0010􀜸􀜤􀜫􀜱 (I)

In an analogous way, a logarithmic relationship was obtained between precipitation intensity (mm),

P, biomass rainfall

retention capacity (%),

R, incorporating a compensation constant (mm), C, the exact value of which will need further

experimental work (Equation II).

􀜴

= 􀵆24.4 ln􁈺􀜲 􀵆 􀜥􁈻 + 115.48 (II)

For the Idbäcken bio-CHP plant situation, these correlations showed the expected average annual precipitation volume to

amount to ~ 8,400 m

3 with ~ 11 % being collected by the drainage ditch. The actual run-off volume contacting with the

biomass was estimated to < 7 % of the same total. In addition, typical run-off routing pathways were quantified showing that,

within 24 h of 15 mm of rain falling on the fuel storage area: ~ 15 % will be collected by the drainage ditch, 0-10 % will be

evaporated depending on seasonal variations and the remaining 75-85 % will stay on the storage area.

Results from the biomass leachate experiments showed on significant differences between filtered respectively non-filtered

samples, which, together with run-off volume data, was seen as an indication that leachate from biomass might not be a

primary contributor to the pollutants found in the drainage ditch. The existence of alternative pollutant sources was further

confirmed by experiments showing concentrations of Pb and N-tot to be significantly higher in water collected from the

drainage ditch than in leachate originating directly from the biomass. As conceivable, albeit not confirmed, pollutant-source

candidates were suggested: dust particles originating from the biomass together with nitrogen fixating bacteria and/or leakage

of ammonium sulfate from a ChlorOut unit installed at the plant. The latter not likely due to run-off routing patterns on plant.

The average concentration levels of most pollutants were found to be below the guideline values currently used as a standard

for stormwater discharged from urban catchment areas.

Measures were recommended as a way to decrease the discharge of contaminants. As one solution was suggested recycling of

the contaminants to the boiler by means of gathering the stormwater and then spraying it onto the stored biomass. With this

method, the plant's flue gas and water treatment system catches the contaminants. Earlier apprehensions regarding this

solution, as this has been considered to increase the load of heavy metals on the boiler, with increased risk for corrosion and

scale formation, are most probably unfounded. This since only 1-2

􀃅 of the total mass fraction of pollutants in biomass have

been proved to be leaching out following as much as 30 mm of rainfall, which, due to high biomass turnover ratios,

practically means that the only factor to worry about is an increased moisture content of the fuel. Alternative suggested ways

of stormwater pollution management included filtration using granulated blast furnace slag, peat and/or bark. Further studies

are recommended to include a more detailed analysis of pollutant content with regards to biomass fine particle fraction as a

mean to further investigate the importance of dust particles for pollutant propagation on plant.

Place, publisher, year, edition, pages
2014.
Keyword [en]
stormwater management, run-off modelling, leachate, biomass, waste
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-158621OAI: oai:DiVA.org:kth-158621DiVA: diva2:778828
Available from: 2015-01-12 Created: 2015-01-12 Last updated: 2017-08-30Bibliographically approved

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