Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: In light of the rapid depletion of the world’s oil reserves, concerns about energy
security prompted the exploration of alternative sources of liquid fuels for
transportation. One such alternative is the production of synthetic fuels with the
indirect coal liquefaction process or Coal-To-Liquids (CTL) process. In this
process, coal is burned in a gasifier in the presence of steam and oxygen to
produce a synthesis gas or syngas, consisting mainly of hydrogen and carbon
monoxide. The syngas is then converted to liquid fuels and a variety of useful
chemicals in a Fischer Tropsch synthesis reactor. However, the traditional
process for syngas production also produces substantial amounts of carbon
dioxide. In fact, only about one third of the carbon in the coal feedstock ends up
in the liquid fuel product using traditional CTL technology. If additional hydrogen
was available, the carbon utilisation of the process could be improved
significantly. The high temperature reactor (HTR) is a gas cooled Generation IV
nuclear reactor ideally suited to provide electrical power and high temperature
heat for the production of carbon neutral hydrogen via high temperature
electrolysis. The integration of an HTR into a CTL process therefore provides an
opportunity to improve the thermal and carbon efficiency of the CTL process
significantly. This thesis presents a possible process flow scheme for a nuclear
assisted CTL process. The system is evaluated in terms of its thermal or syngas
production efficiency (defined as the ratio of the heating value of the produced
syngas to the sum of the heating value of the coal plus the HTR heat input) as
well as its carbon utilisation. If the hydrogen production plant is sized to produce
only enough associated oxygen to supply in the needs of the gasification plant,
syngas is produced at about 63% thermal efficiency, while 71.5% of the carbon
is utilised in this process. It was found that the optimum HTR outlet temperature
to produce hydrogen with a high temperature steam electrolysis process is
850°C. If enough process heat and electrical power are available and process equipment capacities are sufficient, the carbon utilisation of the process could be
improved even further to values in excess of 90%. / AFRIKAANSE OPSOMMING: Die uitputting van die wêreld se olie-reserwes, asook kommer oor energiesekuriteit
het daartoe gelei dat alternatiewe bronne van vloeibare brandstowwe
vir vervoer ondersoek moes word. Een so 'n alternatief is die produksie van
sintetiese brandstof d.m.v. die indirekte steenkool vervloeiing proses of
sogenaamde Coal-To-Liquids (CTL) proses. In hierdie proses word steenkool in
die teenwoordigheid van stoom en suurstof in 'n vergasser gebrand om 'n
sintesegas of singas te produseer, wat hoofsaaklik uit waterstof en
koolstofmonoksied bestaan. Die sintesegas word daarna omgeskakel na
vloeibare brandstowwe en 'n verskeidenheid van nuttige chemikalieë in 'n
Fischer-Tropsch-sintese reaktor. Ongelukkig produseer die tradisionele proses vir
sintesegas produksie ook 'n beduidende hoeveelheid koolstofdioksied. Trouens,
slegs sowat een derde van die koolstof in die steenkool roumateriaal eindig in die
vloeibare brandstof produk indien van tradisionele CTL-tegnologie gebruik
gemaak word. Indien addisionele waterstof beskikbaar was, kon die koolstofbenutting
van die proses aansienlik verbeter word. Die hoë temperatuur reaktor
(HTR) is 'n gas-verkoelde Generasie IV kernreaktor wat by uitstek geskik is om
elektrisiteit en hoë temperatuur hitte te verskaf vir die produksie van koolstofneutrale
waterstof d.m.v. hoë temperatuur elektrolise. Die integrasie van 'n HTR
in 'n CTL-proses bied dus 'n geleentheid om die termiese- en koolstofdoeltreffendheid
van die CTL-proses aansienlik te verbeter. In hierdie ondersoek
word 'n moontlike proses vloeidiagram vir 'n kern-gesteunde CTL-proses
voorgestel. Die stelsel is geëvalueer in terme van sy termiese- of sintesegas
produksie doeltreffendheid (gedefinieer as die verhouding van die hittewaarde
van die geproduseerde sintesegas gedeel deur die som van die hittewaarde van
die steenkool en die HTR hitte-insette) sowel as sy koolstof-effektiwiteit. Indien
die waterstof produksie-aanleg ontwerp word om net genoeg geassosieerde
suurstof te voorsien om in die behoeftes van die vergassing-aanleg te voorsien, word sintesegas teen ongeveer 63% termiese doeltreffendheid vervaardig,
terwyl 71.5% van die koolstof in hierdie proses benut word. Daar is bevind dat
850°C die optimum HTR uitlaat temperatuur is om waterstof d.m.v. hoë
temperatuur stoom-elektrolise te vervaardig. Indien daar genoeg proses hitte en
elektrisiteit beskikbaar is en die proses toerusting kapasiteite voldoende is, sou
die koolstof-benutting van die proses tot meer as 90% verbeter kon word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/71785 |
| Date | 12 1900 |
| Creators | Botha, Frederick Johannes |
| Contributors | Dobson, R. T., Harms, T. M., Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 102 p. : ill. |
| Rights | Stellenbosch University |
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