CTL TECHNOLOGY
COAL FOR THE FT PROCESS
COAL FOR THE FT PROCESS
The chemical content and physical parameters of the coal supply for gasification, prior to the FT processing, will influence the design & operation of the CTL facility.
Carbon forms more than 50% by weight & more than 70% by volume of coal (this includes inherent moisture). This is dependent on coal rank, with higher rank coals containing less hydrogen, oxygen & nitrogen, until 95% purity of carbon is achieved at Anthracite rank & above
COAL CONTENTS
COAL CONTENTS
Volatile matter consists of aliphatic carbon atoms (linked in open chains) or aromatic hydrocarbons (one or more six-carbon rings characteristic of benzene series) and mineral matter
Ash consists of inorganic matter from the earth’s crust:- limestone, iron, aluminum, clay, silica, and trace elements (concentrations of less than 1000 ppm [<0.1% of a rock’s composition] of zinc, copper, boron, lead, arsenic, cadmium, chromium, selenium)
TYPICAL PERCENTAGES OF CONTENT
COAL PHYSICAL PARAMETERS
Ash consists of inorganic matter from the earth’s crust:- limestone, iron, aluminum, clay, silica, and trace elements (concentrations of less than 1000 ppm [<0.1% of a rock’s composition] of zinc, copper, boron, lead, arsenic, cadmium, chromium, selenium)
TYPICAL PERCENTAGES OF CONTENT
COAL PHYSICAL PARAMETERS
Each type of coal has a certain set of physical parameters which are mostly controlled by
- Carbon content
- Volatile content (aliphatic or aromatic hydrocarbons) &
- Moisture
Aliphatic - designating a group of organic chemical compounds (carbon compounds) in which the carbon atoms are linked in open chains
Aromatic - containing one or more six-carbon rings characteristic of the benzene series
Hydrocarbons - numerous organic compounds, such as benzene & methane, that contain only carbon & hydrogen
COAL RANK
The degree of 'metamorphism' or coalification undergone by a coal, as it matures from peat to anthracite, has an important bearing on its physical and chemical properties, & is referred to as the 'rank' of the coal
COAL VOLATILE MATTER
Volatile matter is material that is driven off when coal is heated to 950°C (1,742°F) in the absence of air under specified conditions - liberated usually as a mixture of short & long chain hydrocarbons, & measured practically by determining the loss of weight
Consists of a mixture of gases, low-boiling-point organic compounds that condense into oils upon cooling, & tars
SULFUR IN COAL
Although coal is primarily a mixture of carbon (black) & hydrogen (red) atoms, sulfur atoms (yellow) are also trapped in coal, primarily in two forms. In one form, (1) the sulfur is a separate particle often linked with iron (green, pyritic sulfur) with no connection
to the carbon atoms, as in the center of the drawing (fools gold). In the second form, (2) sulfur is chemically bound to the carbon atoms (organic sulfur), such as in the upper left
GASIFICATION BASICS
PRODUCTS OF GASIFICATION
BEGINNINGS OF THE FT PROCESS
The process was invented in petroleum-poor but coal-rich Germany in the 1920s, to produce liquid fuels. The invention of the original process was developed by the German researchers Franz Fischer and Hans Tropsch at the Kaiser Wilhelm Institute. It was used by Germany and Japan during World War II to produce alternative fuels. Germany's annual synthetic fuel production reached more than 124,000 barrels per day in 1944 (from 25 plants, 6.5 million tons)
FT PROCESS BASICS
The Fischer-Tropsch process uses hydrogen (H2) and carbon-monoxide (CO) to make different types of hydrocarbons with various H2:CO ratios
In a CTL facility the H2 and CO can be supplied from the coal gasifier
FT PROCESS BASICS
The original Fischer-Tropsch process is described by the following chemical equation:
The initial FT reactants in the above reaction (i.e. CO & H2) can be produced by other reactions such as the partial combustion of a hydrocarbon or by the gasification of coal or biomass:
The FT process still produces CO2 although substantially smaller amounts compared with the gasification process
The products of FT synthesis include hydrocarbon chains, oxygenates, water & carbon-dioxide among others at varying proportions depending on the catalyst used & reactor conditions. The efficiency of the FT reaction is commonly measured by the conversion ratio, also known as the rate of FT reaction
SLURRY- PHASE FT REACTOR
FT & CATALYSIS
The FT Process is a catalyzed chemical reaction in which carbon monoxide and hydrogen are converted into liquid hydrocarbons of various forms
The catalyst used (often based on iron or cobalt) is a chemical compound that increases the rate of a chemical reaction without altering the final equilibrium (catalysis is purely a kinetic phenomenon). Catalysts reduce the free activation energy which then quickens the speed of the reaction
M = Metal
CO = Carbon Monoxide
The ligand CO (propensity to bonding) exchanges electrons with the Metal
The ligand CO (propensity to bonding) exchanges electrons with the Metal
CATALYSTS & PRODUCTS
CATALYST | PRODUCT
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Iron | Linear alkenes and oxygenates
Cobalt | Alkanes
Nickel | Methane
Ruthenium | High molecular weight hydrocarbons
Rhodium | Large amounts of hydrocarbons & little oxygenates
Note: Alkanes are hydrocarbons containing only single covalent bonds. Alkenes are hydrocarbons containing a double covalent bond between two carbon atoms. Oxygenated substances have been infused with oxygen. Oxygenates are usually employed as gasoline additives to reduce CO that is created during the burning of the fuel
CTL GLOBAL PRODUCTION RATES
1944 Germany’s production = 124,000 B/D
1944 Germany’s production = 124,000 B/D
PRODUCTS FROM A BARREL OF CRUDE OIL
One barrel of crude oil produces nearly half a barrel of gasoline
Source: http://www.answers.com/heat%20in%20one%20barrel%20of%20oil
Numbers are based on average yields for U.S. refineries in 2000. One barrel contains 42 gallons of crude oil. The total volume of products made is 2.6 gallons greater than the original 42 gallons of crude oil. This represents ‘processing gain’
WHAT CAN BE PRODUCED FROM A CTL FACILITY?
The final products coming from a CTL facility are decided upon during the initial stages of plant design
Source: Brian H. Bowen, Marty W. Irwin, Devendra Canchi - The Energy Center at Discovery Park Purdue University
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