combustion and related topics

MSc Thesis projects available starting June 2018

 

Department Process and Energy, Section Fluid Mechanics

Prof. Dr. Dirk Roekaerts, Process & Energy Department 

Section Fluid Mechanics, d.j.e.m.roekaerts@tudelft.nl, Office: 34K-0-170.

 

All projects are theory and modeling projects and are in some way or another related to turbulent reacting flow.

 

1. Turbulent combustion in supercritical water (hydrothermal flames) 

2. Modeling of pyrolysis oil atomization, coking, evaporation and combustion

3. Heat transfer and pollutant formation in cook stoves

4. Modeling of hydrogen production by cracking of methane in a solar reactor

5. Modeling of metal dust flames

6. Modeling of hydrogen combustion

 

1. Theory and modelling of turbulent combustion in supercritical water (hydrothermal flames) 

 

Introduction

Supercritical water oxidation or SCWO is a process that occurs in a mixture of water and other substances at temperatures and pressures above the thermodynamic critical point. At supercritical conditions the behaviour of water as a solvent is altered so that chlorinated hydrocarbons become soluble in the water, allowing single-phase reaction of aqueous waste with a dissolved oxidizer. Gasification of wet biomass recently has been subject of experimental and systems studies at the P&E department and this project can provide theoretical support for those studies.

 

Flames in fuel/water mixtures at supercritical conditions are known as hydrothermal flames. ETH Zurich has pursued the investigation of these “hydrothermal flames” experimentally in continuously operated reactors. Compared to regular gaseous flames the situation is different because the ideal gas equation of state is no longer valid and has to be replaced, kinetic rates are different and material properties are different. New phenomena arise. 

 

Project

The objective of this project is to formulate the theoretical equations describing hydrothermal flames in turbulent conditions. This will involve combining all relevant transport equations, appropriate equation of state, turbulence model, chemical model and turbulence-chemistry interaction model. Validation will be done with the experimental results of ETH Zurich. Base case simulations can be made using a commercial CFD code, like ANSYS-Fluent. But in a next step advanced turbulence-chemistry interaction models implemented in an in-house CFD code ‘PDFD’ will be used. In this way the question can be answered what are the key phenomena determining ignition behaviour, heat release and burnout. The work builds on our ongoing research on hydrothermal combustion in laminar flames.

 

 

 

2. Modeling of pyrolysis oil atomization, coking, evaporation and combustion

 

Pyrolysis oil is can be produced by condensation of gases released by solid biofuel heated in the absence of oxygen. In principle it is a more convenient biofuel than the original biomass (lower water content, higher energy density and easier to transport). However, using pyrolysis oil in combustion systems is not so easy. Its high viscosity makes good atomization into droplets difficult. Heating of the fuel to lower viscosity is not possible because of polymerization reactions leading to a fuel prone to coking, char formation and related particulate emissions. Therefore burner design must satisfy more stringent requirements than for fossil fuel. To enable systematic development of clean pyrolysis combustion technology, accurate models are needed for pyrolysis oil droplet heating, (partial) evaporation and chemical transformation. In a second step these can be integrated in simulations of typical droplet trajectories in a combustor or gas turbine. 

 

Project 

This project will setup and validate models for pyrolysis oil combustion. Good knowledge is required of transport phenomena and thermodynamics of phase equilibrium in mixtures. Validation will be made using literature data on ‘synthetic biofuels’ with properties resembling those of pyrolysis oil. The work builds on a previous MSc project in which evaporation models for a multicomponent fuel mimicking pyrolysis oil was investigated.

 

3. Understanding the flow, reaction and heat transfer in cook stoves

 

Introduction

Many people in the world (estimated to be around 2.7 billion) depend on traditional forms of stoves for cooking food. This represents a large amount of energy: the worldwide share of traditional biomass in domestic energy use is 30%. But the design and use of cook stoves is not optimal. Emission of particulate matter (smoke) and pollutant gases like CO from biomass cook stoves has an adverse impact on the health of the users and their family.  Hence, design of new cookstoves that improve cooking performance and reduce harmful emissions, specifically particulate matter (PM) is an active area of research. Recently deposit of biochar has been proposed for soil regeneration also towards lowering of CO2 levels in the atmosphere. When net biochar production is added as objective, the cookstove design will also be affected.

 

Project

This project will investigate the fundamental aspects of cook stove operation. This involves setting up a model for processes in a bed of solid biomass pellets (heating, pyrolysis, and gasification and combustion of gases in the space above the bed with optimal heat transfer as the main aim. 

 

The first step consists in making the inventory of important conversion and transport phenomena to identify the important issues. The second step involves reacting flow simulations of a typical configuration. Studies reported in the literature are restricted to standard steady state turbulence models with simple turbulence-chemistry interactions. A higher accuracy can be reached by using state-of-the-art models including large eddy simulation, systematically reduced chemistry, and statistical models for turbulence-chemistry interaction. The final aspect is optimization. E.g. one method for improving cooking performance and reducing emissions is using air injection to increase turbulence of unburned gases in the combustion zone.  Air injection reduces total PM mass emissions. 

The research program proposed above it too large for a single MSc thesis project and a more specific program will be formulated at the start of the project.

 

 

4. Production of hydrogen in a solar thermal reactor.

In the solar reactor for cracking of methane, solar energy is used to split methane in hydrogen and carbon. The carbon can be use as product (carbon black), converted in a direct carbon fuel cell or can be sequestered. The hydrogen is a valuable product for further use in chemical processes or energy conversion. The physical processes in the solar reactor involve radiation, dispersed multiphase flow and chemical reaction. 

 

In previous studies in the literature it was demonstrated that to range long duration stable operation of the solar reactor, special attention has to be given to the flow patterns in the reactor. To avoid clogging the carbon particles should not deposit on the walls. Computational studies have been made on the non-reacting flow in a “vortex reactor”. Now also the reacting flow in this reactor has to be studied in order to guide experiments and to support the development of scaling rules. In a CFD approach the coupled problem of radiation, turbulent multiphase flow and chemical reaction will be studied. 

 

Project

CFD simulations will be made of model solar reactor. The validation will be made using available experimental data from literature. The study can either be more fundamental keeping the flow geometry simple or more application oriented and using a reactor geometry close to what will be needed in practice. The aim is to be able to predict conversion and efficiency of the reactor for a relevant range of conditions. The CFD software used and or the amount of programming depends on the type of reactor that will be studied.

                                   

5. Modeling of metal dust flames

Combustion of clouds of metal particles is of interest for several reasons. In the context of ‘dust explosions’ it has become clear that metal dusts have to be considered a special class of dust due to their high flame temperature and high heat release. On the other hand metal fuels have been proposed as an alternative to fossil hydrocarbon fuel combustion. Combined with reduction of the metal-oxide a closed cycle is formed with no net CO2 emission.

 

To understand the combustion of clouds of metal particles basic understanding of flame propagation in a metal dust / air mixture is needed. A laminar dust flame created on a labscale dust burner provides access to measurements of the laminar flame speed of metal dusts for a range of equivalence ratios. Such measurements are available in the literature. Interesting transitions between different types of flame occur. The project aims at simulating  laminar dust flames and to validate the results with experiments. In order to do so extensions from existing in-house codes for gaseous flames and spray flames will be used.  

 

6. Modeling of hydrogen combustion

 

Hydrogen could play an important role in the energy transition. This has been elaborated in detail in the document “Contouren van een routekaart waterstof” published by TKI Nieuw Gas in March 2018.

Focusing only on combustion of hydrogen, leaving aside other useful applications, several application areas can be identified: combustion of hydrogen for production of high temperature heat and for low temperature heat, 

 

The aim of this project is to 

 

High temperature heat is needed in industrial processes in several industrial sectors, most importantly petro-chemical industry and steel industry.

 

In industry often hydrogen rich gases are formed (e.g. in oil refining, in cokes production, in electrolysis of salt in water). These gases most often are used direclty or mixed with natural gas in boilers and furnaces for the production of steam an high temperature process heat, or for the production of electricity in power plants. 

 

 

The technology used for combustion of these gases will have to be further developed for several reasons. To start with, since emission legislation is tightening the current generation of burners will not be effective and low emission systems have to be developed. This can be considered continuation of existing research lines. 

 

More important changes are expected however. With the suppression of fossil fuel the available fuel mix will change and the heat transfer applications will have to cope with that. A hydrogen rich fuel mix, eventually pure hydrogen, might be possible. This will induce changes in burner operation, radiative heat transfer and emissions. 

 

To start with, the current industrial combustion should be reviewed with their current use of hydrogen and ability to handle large fractions of hydrogen. 

 

 

MSc projects in combustion

Chair:
Fluid Mechanics

Involved People:
prof.dr.ir. D.J.E.M. Roekaerts