| 1. |
- Bozaghian Bäckman, Marjan, et al.
(författare)
-
Bed material performance of quartz, natural K-feldspar, and olivine in bubbling fluidized bed combustion of barley straw
- 2024
-
Ingår i: Fuel. - : Elsevier. - 0016-2361 .- 1873-7153. ; 364
-
Tidskriftsartikel (refereegranskat)abstract
- The present study investigates how three different silicate-based bed materials behave in bubbling fluidized bed combustion of a model agricultural residue with respect to ash composition, namely barley straw. Quartz, natural K-feldspar, and olivine were all used in combustion at 700 °C, and the resulting layer formation and bed agglomeration characteristics were determined. Based on this, a general reaction model for bed ash from agricultural residues was proposed, taking into account the reactivity of the different silicates investigated towards the main ash-forming elements K, Ca, and Si. The proposed reaction model links bed material interaction with K-rich bed ash to the degree of polymerization of the silicate bed material, where addition reactions occur in systems with high polymerization, predominately in quartz, and substitution reactions dominate for depolymerized silicates such as K-feldspar and olivine.
|
|
| 2. |
|
|
| 3. |
- Bozaghian, Marjan, et al.
(författare)
-
Combustion characteristics of barley straw stored with CaCO3 during fluidized bed combustion using quartz and olivine as bed materials
- 2017
-
Konferensbidrag (refereegranskat)abstract
- In order to achieve a continuous feedstock supply for power plants a large quantity of harvested material must be stored for long-term periods. During storage, especially during right conditions of temperature, moisture and oxygen, solid agricultural fuels are susceptible to microbial activities. Microbial respiration not only leads to loss of organic carbon, but also to an increased temperature in the stored fuel which may lead to self-ignition. There is on-going work studying the effect of adding Ca as CaO or CaCO3 during storage of straw with the aim of creating an unfavorable alkaline microenvironment that prevents microbial growth during storage. The effect of this amendment during storage is still being explored, but the effect in the combustion step of the process in terms of determining the potential of Ca-additives to positively affect overall ash chemistry have yet to be certainly quantified. Utilization of agricultural crops for energy purposes in heat and power plants has proven to be challenging in numerous ways. Compared to woody fuels, agricultural fuels can cause severe ash-related operational problems in combined heat and power plants through by fouling, slagging and/or bed agglomeration due to their high concentrations of inorganic constituents. The objective of the present study is therefore to determine the fouling and bed agglomeration characteristics during fluidized-bed combustion of barley straw stored with different dosages of Ca to biomass with the main ash-forming elements shown in Figure 1, using two types of bed materials, quartz and olivine.
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
- Bozaghian, Marjan, et al.
(författare)
-
Combustion characteristics of straw stored with CaCO3 in bubbling fluidized bed using quartz and olivine as bed materials
- 2018
-
Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 212, s. 1400-1408
-
Tidskriftsartikel (refereegranskat)abstract
- The addition of Ca-containing compounds can reduce mass loss from agricultural biomass during storage. The resulting alkaline environment is detrimental to microorganisms present in the material. Theoretical analysis of Ca-containing biomass suggests that combustion properties are improved with respect to slagging. To validate the theoretical calculations, barley straw was utilized as a typical model agricultural biomass and combustion characteristics of straw pre-treated with 2 and 4 w/w% CaCO3 for combined improvement of storage and combustion properties were determined through combustion at 700 degrees C in a bench-scale bubbling fluidized-bed reactor (5 kW) using quartz and olivine sand as bed materials. The combustion characteristics were determined in terms of elemental composition and compound identification in bed ash and bed material including agglomerates, fly ash, particulate matter as well as flue gas measurements. The addition of CaCO3 to straw had both positive and negative effects on its combustion characteristics. Both additive levels raised the total de fluidization temperature for both quartz and olivine, and olivine proved to be less susceptible than quartz to reactions with alkali. With Ca-additives, the composition of deposits and fine particulate matter changed to include higher amounts of KCl potentially leading to higher risk for alkali chloride-induced corrosion. Flue gas composition was heavily influenced by CaCO3 additives by significantly elevated CO concentrations likely related to increased levels of gaseous alkali compounds. The results suggest that it is necessary to reduce gaseous alkali compounds, e.g. through kaolin or sulphur addition, if alkali-rich straw is to be co-combusted with Ca-rich biomass or large amounts of Ca-additives.
|
|
| 7. |
- Bozaghian, Marjan, et al.
(författare)
-
Does mechanical screening improve fuel properties? Effects of mechanical screening of stored logging residue chips on ash chemistry and other parameters relevant for combustion
- 2019
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Forestry and the forest industry plays an important role in the Swedish economy. From forest operations and at sawmills and pulp and paper mills several by-product assortments are generated and these are providing the basis for the highly developed Swedish bioenergy sector. Logging residues constitute a major resource and is utilized as fuel in heat and power plants. However, due to a relatively low heating value and high management costs, this resource is still underutilized. Logging residue chips have irregular particle size, high moisture content (30-60%) and high ash content (8-15 %) and these features cause most of the problems encountered during the operation of feeding systems and combustion processes. Ash, present both in endogen plant tissues and as extrinsic matter such as sand and clay minerals, is of especially big concern for small-size plants. In this on-going work screening of logging residue chips was performed. Different mechanical screening methods was applied with the aim to provide a homogenous fuel with a higher quality for combustion purposes. Through screening, the chemical fuel composition is also altered and this affects combustion behavior and ash chemistry. The objective of the present study is to, from a combustion process perspective with emphasis on ash chemistry, evaluate the overall effects of different screening procedures when applied on stored logging residue chips.
|
|
| 8. |
- Bozaghian, Marjan, et al.
(författare)
-
Does Mechanical Screening of Contaminated Forest Fuels Improve Ash Chemistry for Thermal Conversion?
- 2020
-
Ingår i: Energy and Fuels. - : American Chemical Society (ACS). - 0887-0624 .- 1520-5029. ; 34, s. 16294-16301
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of mechanical screening of severely contaminated forest fuel chips was investigated, focusing on main ashforming elements and slagging tendency and other properties with relevance for thermal conversion. In this study, screening operations were performed according to practice on an industrial scale by combining a star screen and a supplementary windshifter in six different settings and combinations. Mechanical screening reduced the amount of ash and fine particles in the accept fraction. However, the mass losses for the different screening operations were substantial (20−50 wt %). Fuel analyses of the non-screened and the screened fuels showed that the most significant screening effect was a reduction of Si and Al, indicating an effective removal of sand and soil contaminations. However, the tested fuel’s main ash-forming element’s relative concentration did not indicate any improved combustion characteristics and ash-melting behavior. Samples of the accept fractions and non-screened material were combusted in a single-pellet thermogravimetric reactor, and the resulting ashes’ morphology and elemental composition were analyzed by scanning electron microscopy−energy dispersive X-ray spectrometry and the crystalline phases by powder X-ray diffraction. Results from both these analyses confirmed that screening operations had no, or minor, effects on the fuels’ ash chemistry and slagging tendencies, i.e., the fuels’ proneness to ash melting was not improved. However, the reduction of ash and fine particles can reduce slagging and other operational problems in smaller and more sensitive combustion units.
|
|
| 9. |
- Bozaghian, Marjan
(författare)
-
Lignocellulosic residues for bioenergy : effects of storage, fuel design, and combustion characteristics
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Utilization of lignocellulosic residues for bioenergy raises storage, handling, and combustion challenges. The ash-forming elements in biomass may cause ash-related problems during combustion, such as slagging, fouling, corrosion, or bed agglomeration. Most of these problems are linked to ash-chemical reactions involving alkali. The overall objective of this thesis was to evaluate the impact of storage, fuel design measures, and process adaptation for improving combustion characteristics of lignocellulosic residues to mitigate ash-related operational problems. This was done by monitoring storage-induced changes in bark influencing final material characteristics. Mechanical screening and Ca-additivation on forest and agricultural residues were done as a fuel design measure. In addition, the performance of different bed materials was evaluated in bubbling fluidized bed combustion. Significant changes in the lignocellulosic matrix near pile surfaces were observed during storage of bark, and these changes will not affect the combustion characteristics. Screening efficiently reduced the amount of ash but was associated with significant fuel mass losses and did not change the ash chemistry; thus, combustion characteristics and ash melting behavior can be expected to remain unchanged. The Ca-addition significantly increased the total defluidization temperatures but implied an elevated risk for forming corrosive species and high CO (g) concentrations. High interactions between fuel ash and quartz bed particles and low interactions between fuel ash, olivine, and feldspar bed particles were observed. The feldspar bed material reduced defluidization temperature due to the increased amount of alkali in the bed by diffusion of alkali from feldspar grains. Overall, a good understanding of the ash transformation reactions is needed to mitigate ashrelated problems. In addition, fuel design measures must affect the ash chemistry in the fuel to be worthwhile.
|
|
| 10. |
- Xiong, Shaojun, et al.
(författare)
-
Calcium oxide as an additive for both conservation and improvement of the combustion properties of energy grass : A preliminary study
- 2017
-
Ingår i: Biomass and Bioenergy. - : Elsevier. - 0961-9534 .- 1873-2909. ; 99, s. 1-10
-
Tidskriftsartikel (refereegranskat)abstract
- Degradation of biomass is one of the major reasons for high costs of feedstock collection, transport, and storage, which is largely associated with biomass moisture and microbial activities. Our concept is to add calcium oxide (CaO) to the biomass already when it is collected and in its natural (wet) condition. When a suitable quantity of CaO is added to moistened biomass, an alkali microenvironment will be formed with a pH exceeding 9, based on the reaction CaO + H2O ↔ Ca(OH)2. As a consequence, microbial activities are largely inhibited. The Ca(OH)2 will then successively react with CO2, following the reaction Ca(OH)2 + CO2 ↔ CaCO3 + H2O. The CaCO3 will reside in the feedstock throughout the entire production chain and end up as an additive/sorbent to improve combustion by decreasing slagging. Two experiments were conducted and proved the concept works for at least reed canary grass, but, as expected, the strength of the effect was dependent on the CaO dosage and initial biomass moisture.
|
|
