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Producer Gas Implementation in Steel Reheating Furnaces from Lab to Industrial Scale: A Computational Fluid Dynamics and Thermodynamics Approach
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.ORCID iD: 0000-0002-5976-2697
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The integrated steel-making plants in Sweden contributed with approximately 8 % of the total CO2 emissions in the country in 2011. A major contributor to these emissions is the combustion of fossil fuels in different process units. Therefore, it is essential to reduce emissions by limiting the fossil fuels consumption in the steel industry. A possible solution to reduce the emissions is to implement alternative fuels, which are produced from various combustion and gasification sectors in the iron and steel-making industry. Currently, the blast furnace gas (BFG) and coke oven gas (COG) are extensively used for district heating purposes. Depending on the availability of biomass in a region, gasified biomass (Syngas) can also be used as an alternative fuel source. In addition, the extracted energy from these producer gases can be used in other heat treatment processes such as reheating furnaces. However, these producer gases contain several impurities such as, alkali metals, halogens, particulate matter, sulfur compounds and other mineral contaminants, which can be problematic. For instance, in the steel reheating furnaces, these impurities can form sticky layers of solutions on the steel slab surfaces which are not easy to remove.

            The High Temperature Agent Combustion (HiTAC) technology has several advantages compared to the conventional methods. These include temperature uniformity, a flexibility of fuels, low pollutant emissions and a volumetric combustion. In this study, these factors have been investigated for the pulverized coal combustion, when the coal particles are assumed to follow a Rosin-Rammler distribution. Moreover, due to the mentioned superior properties of HiTAC technique, it has also been applied for the combustion of producer gases as alternative fuel for steel reheating furnaces.

            A coupled Computational Fluid Dynamics (CFD) and thermodynamics approach has been developed to analyze the combustion of producer gases and the behavior of impurities in these gases for the steel reheating furnaces. The obtained results prove the capability of HiTAC technique to be used for the combustion of producer gases by enhancing the temperature and by reducing the size of steel reheating furnaces. The findings also show that the Low Calorific Value (LCV) of BFG and the presence of 52 % nitrogen in the gas are responsible for a lower heat release in comparison to other producer gases.

            The impurities in steel reheating furnaces are considered as ash particles having a particle size distribution similar to the pulverized coal particles. The accumulation of the ash particles at the steel slab surface is predicted using the CFD simulations. Furthermore, the thermo-chemical calculations are used to understand the effect of all the involved chemical compositions in an equilibrium thermodynamics system of impurities and iron-oxides. This thermodynamics study of impurities is divided in two steps. In the first study, at the steel slab surface, the temperature gradients and the concentration of impurities are not considered. This investigation is carried out to identify the reactivity and phase transformation of different ash mineral components with respect to the temperature zones (preheating, heating and soaking) in steel reheating furnaces. Here, chloride compounds are the most reactive compounds in comparison to other impurities. It is also found that an increased temperature from the preheating zone up to the soaking zone leads to an increased iron-oxide formation. In the heating and soaking zones, an addition of mineral compounds like SiO2 and CaO is also found to accelerate the formation of the sticky solutions at the steel slab surface. Moreover, by increasing the steel slab temperature the formations of sticky layers are highly abated in the late heating zone and the entire soaking zones.

            In the second study the concentration of particles, density of particles and temperature gradients at the steel slab surface are taken into account. Thereby, the shortcomings of the first thermodynamics system are improved. It is found that for the considered furnace configuration, the particles received the same velocity as the injected fuel (70 m/s) and they are heated up to a temperature of 1600 °C. The most of the particles, with the average size of 50 µm, are evacuated through the exhaust ports due to the inertial dominant force. Only around 10 percent of these particles have a tendency to stick to the steel slab surface at the heating zone rather than at the soaking zone. These findings could be applied for improvements in the combustion systems and furnace designs to reduce unwanted accumulations and hot-spots of sticky layers on the steel slab surface. This information may also be useful for planning of new investments in gas cleaning systems, if producer gases are used as fuels.

Abstract [sv]

2011 stod ståltillverkningen för ungefär 8 % av de totala CO2 utsläppen i Sverige, varav en bidragande orsak till utsläppen är förbränningen av fossila bränslen i olika processer. På grund av den stora mängden CO2 utsläpp så är det viktigt begränsa förbrukningen av fossila bränslen inom stålindustrin. En av de möjliga lösningarna är användning av alternativa bränslen, såsom processgaser som skapas vid förbränning och förgasning i tillverkningen av järn och stål. För tillfället så änvänds denna typ av gaser för produktion av fjärrvärme. En annan möjlighet är att använda sig av förgasad biomassa (syngas) som alternativ bränslekälla. Dessutom så kan energin från processgaserna återanvändas i andra värmebehandlingsprocesser, såsom ämnesugnar. Dessvärre så innehåller dessa gaser föroreningar såsom alkalimetaller, halogener, partiklar, svavelföreningar och andra mineralföroreningar. Förekomsten av dessa orsakar problem vid återanvändning. Till exempel så kan dessa föroreningar bilda kladdiga föreningar på stålämnets ytor i ämnesugnar och dessa är svåra att avlägsna från stålytan i ett senare skede.

            Högtemperaturförbränningsteknologi (HiTAC) har många fördelar jämfört med konventionella metoder, såsom en jämn temperaturfördelning, en stor bränsleflexibilitet, låga utsläpp av föroreningar och en volymetrisk förbränning. I denna undersökning så har dessa faktorer undersökts för kolpulverförbränning, där kolpartiklarna har antagits ha en Rosin-Rammler distribution. På grund av dessa fördelar så har HiTAC metoden också undersökts för förbränning av processgaser i ämnesugnar.

En kombination av fluiddynamikberäkningar (CFD) och termodynamiska metoder har använts för att analysera förbränningen av producerade gaser och det resulterande beteendet hos föroreningarna vid uppvärmning av stål i ämnesugnar. Resultaten visar att HiTAC kan användas för förbränning av processgaserna och därmed öka temperaturen och minska storleken på ämnesugnarna. Resultaten visade också att lågförbränningsvärdet (LCV) av masugnsgas och det 52 %-iga kväveinnehållet i gasen resulterar i ett lägre värmevärde jämfört med andra producerade gaser.

            Föroreningarna i ämnesugnar för stål anses vara askpartiklar med samma partikelfördelning som de som skapats vid förbränningen av kolpartiklarna. Med hjälp av CFD simuleringarna förutsågs ackumuleringen av askpartiklarna på stålämnets yta. Vidare så utfördes de termokemiska beräkningar för att förstå effekten av den kemiska sammansättningarna hos föroreningarna och järnoxiderna i ett termodynamiskt system i jämvikt. Den termodynamiska undersökningen är indelad i två steg. I det första steget så tas inte temperaturgradienter eller koncentrationsgradienter av föroreningar vid stålytan i beaktning. Detta görs för att identifiera reaktiviteten och fasomvandlingen hos olika askkomponenter för de olika temperaturzonerna (förvärming, värmning och utjämningszon) i ämnesugnen. Beräkningarna visade att klorföreningar är de mest reaktiva föroreningarna och att en ökad temperatur från mörkzonen förvärmningstill utjämningszonen leder till en ökad mängd järnoxider. Förekomst av SiO2 och CaO i värmning och utjämningszonen påskyndar bildandet av kladdiga föreningar på stålämnets yta. Genom att öka stålämnets temperatur så avtar bildandet av kladdiga föreningar i slutskedet av värmningszonen och för hela utjämningszonen.

            I det andra steget så tas koncentrationen och densiteten hos partiklarna och även temperaturgradienter vid stälämnets yta i beaktande. Därigenom så har bristerna från det första termodynamiska systemet förbättrats. Resultaten visade att för den aktuella ugnskonfigurationen så hade partiklarna samma hastighet som det injicerade bränslet (70 m/s) och att de uppvärmdes till en temperatur på 1600 °C. De flesta av partiklarna, med en storlek på 50 µm, lämnar ugnen genom avgasöppningarna på grund av den dominerande tröghetskraften. Det är bara omkring 10 procent av dessa partiklar som tenderar att fastna på stålämnets yta i värmningszonen snarare än i utjämningszonen. Resultaten från denna studie kan användas för att förbättra förbränningssystemet och ugnsdesignen för att reducera oönskade ansamlingar av kladdiga föreningar på stålämnets yta. Informationen kan också vara användbar för planering av nya investeringar i gasrengöringssystem, där produktionsgaser används som bränsle.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. , 84 p.
National Category
Energy Engineering
Research subject
Materials Science and Engineering
Identifiers
URN: urn:nbn:se:kth:diva-187248ISBN: 978-91-7595-975-7OAI: oai:DiVA.org:kth-187248DiVA: diva2:929400
Public defence
2016-06-09, Sal B3, Brinellvägen 23, Stockholm, 09:00 (English)
Opponent
Supervisors
Note

QC 20160519

Available from: 2016-05-19 Created: 2016-05-18 Last updated: 2016-05-19Bibliographically approved
List of papers
1. Performance of pulverized coal combustion under high temperature air diluted by steam
Open this publication in new window or tab >>Performance of pulverized coal combustion under high temperature air diluted by steam
2014 (English)In: ISRN Mechanical Engineering, ISSN 2090-5122, E-ISSN 2090-5130, Vol. 2014Article in journal (Refereed) Published
Abstract [en]

The high temperature air combustion (HiTAC) is an advanced promising technology for heat recovery, energy saving, and stability improvement of flame. Computational fluid dynamic (CFD) is known as an applied tool to execute HiTAC modeling. In this paper, performances of pulverized coal combustion under the high preheated and oxygen deficient air are studied by both experimental and numerical methodology. The experimental facilities have been accomplished in a HiTAC chamber with coal injection velocity that ranges from 10 to 40 m/s. In order to achieve different preheated temperatures, the combustion air in such system is diluted by variable steam percentages from 0 to 44%. Results of mathematical simulation and experimental tests present convincible agreement through whole region. It is concluded that NOX emission is reduced by increasing the steam percentage in the oxidizer due to decreasing the flame temperature. Besides, graphical contours show that by adding more steam to oxidizer composition, the oxygen concentration decreased. Additionally, results show that when the injection speed of fuel is increased, NOX emission is also increased, and when the injection rate of preheated air is increased, NOX emission shows decreasing trend. Further contribution in future is needed to investigate the performance of such technologies.

National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-161019 (URN)10.1155/2014/217574 (DOI)2-s2.0-84899575200 (ScopusID)
Note

QC 20150313

Available from: 2015-03-13 Created: 2015-03-06 Last updated: 2016-05-19Bibliographically approved
2. On the Implementation of Producer Gases as Alternative Fuels in Steel Reheating Furnaces
Open this publication in new window or tab >>On the Implementation of Producer Gases as Alternative Fuels in Steel Reheating Furnaces
Show others...
2015 (English)In: Proccedings of ASME 2015 International Mechanical Engineering Congress and Exposition / [ed] ASME, Houston, Texas, USA, November 13–19, 2015: ASME Press, 2015, Vol. 6AConference paper (Refereed)
Abstract [en]

During the past decades, combustion of producer gases from other facilities has been introduced as one of the promising techniques in steel furnaces. The impurities inside producer gases are responsible for a low quality steel production due to formation of the molten ash that forms sticky layers of solutions on steel surfaces. Therefore, a comprehensive investigation is needed before a full implementation of producer gases inside the industrial furnaces. In this paper, the effects of impurities inside the gasified biomass flue gases are thermodynamically investigated regarding temperature zones inside a reheating furnace. After that, the high temperature agent combustion (HiTAC) is investigated as a solution for a steel batch reheating furnace to reduce the side effects of using the producer gases. Finally, computational fluid dynamics (CFD) is used as a numerical technique to compare four different producer gases in the studied furnace. The temperature distribution is validated with existing literature data. It shows a good agreement with a 5% error in the heating and a 10% error in the soaking zones of the reheating furnace. The comparison of simulation results assists in the understanding of the chemical and thermal behavior of different gases and provides useful data for the furnace fuel optimization.

Place, publisher, year, edition, pages
Houston, Texas, USA, November 13–19, 2015: ASME Press, 2015
Keyword
Gases, Steel, Fuels, Furnaces
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-187243 (URN)10.1115/IMECE2015-51692 (DOI)978-0-7918-5743-4 (ISBN)
Conference
ASME 2015 International Mechanical Engineering Congress and Exposition,Houston, Texas, USA, November 13–19, 2015
Note

QC 20160520

Available from: 2016-05-18 Created: 2016-05-18 Last updated: 2016-05-20Bibliographically approved
3. A thermodynamic study of hot syngas impurities in steel reheating furnaces: Corrosion and interaction with oxide scales
Open this publication in new window or tab >>A thermodynamic study of hot syngas impurities in steel reheating furnaces: Corrosion and interaction with oxide scales
Show others...
2014 (English)In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 77, 352-361 p.Article in journal (Refereed) Published
Abstract [en]

Environmental concerns lead industries to implement gasified biomass (syngas) as a promising fuel in steel reheating furnaces. The impurities of syngas as well as a combination with iron oxide scale form complex mixtures with low melting points, and might cause corrosion on steel slabs. In this paper, the effects of syngas impurities are thermodynamically investigated, when scale formation on the steel slabs surface simultaneously takes place. A steel reheating furnace can be divided into preheating, heating, and soaking zones where the temperature of a steel slab changes respectively. Therefore, the thermodynamic calculation is performed at different temperatures to predict the fate of impurities. Then, the stable species are connected with respective zones in a reheating furnace. It is concluded that reactions due to alkali compounds, chloride, and particulate matter could take place on steel slabs. In the low temperature range, interaction of sodium chloride occured with pure iron prior to scale formation. Then, at high temperature the reactions of impurities are notable with iron oxides due to scale growing. Furthermore, the multicomponent reactions with syngas impurities showed that most of alkali contents evaporate at first stages, and only small amounts of them remain in slag at high temperature.

Keyword
Reheating furnace, Thermodynamic calculation, Syngas, Impurities, Alkali compounds
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-160083 (URN)10.1016/j.energy.2014.08.092 (DOI)000346542500040 ()2-s2.0-84909646337 (ScopusID)
Funder
Swedish Energy Agency, 35386-1
Note

QC 20150225

Available from: 2015-02-25 Created: 2015-02-13 Last updated: 2016-05-19Bibliographically approved
4. On Thermochemical Behaviors of Ash Particles during Combustion of Producer Gases inside a Steel Reheating Furnace
Open this publication in new window or tab >>On Thermochemical Behaviors of Ash Particles during Combustion of Producer Gases inside a Steel Reheating Furnace
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The use of producer gases from gasification and combustion of fossil fuels and biofuels in steel reheating furnaces represents a promising future application. Prior to the direct implementation of such gases as an alternative fuel for high quality steel products, a comprehensive thermochemical study of possible impurities inside the furnace is crucial. This is especially important for heating of high quality steel products. Ash is one of these impurities, which contains particular compounds like Sodium (Na), Potassium (K), Chloride (Cl), and other minerals. The depositions of these compounds, which cause a formation of sticky layer of solutions on the steel slabs surface, are responsible for low quality products. Furthermore, it is a challenge and energy consuming process to remove these elements from the slabs. In this paper, the combustion of a producer gas mixture including ash particles inside a batch type steel reheating furnace has been investigated. In the first step, a computational fluid dynamics (CFD) approach is utilized to investigate the feasible locations of ash particles at the interface layer of the flaring gas media and the steel slab surface. After that, result from thermodynamic calculations considering the slab temperature, particle concentrations, ash compositions, and its reactions with the steel slab are presented. The results show that the concentration of particles is highly dependent on the flow field, slab temperature, as well as their size distribution. Also, the most probable places of particles at the interface layer of flaring gas media and the steel slab surface is primarily found near the steel slab cross sectional sides in the heating zone. It is believed that the present results could be helpful for a further optimization of furnace and combustion system design.

National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-187244 (URN)
Note

QC 20160519

Available from: 2016-05-18 Created: 2016-05-18 Last updated: 2016-05-19Bibliographically approved

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