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SS17_I: Bioenergy Technology > Doris-BtL Fuels > Flashcards

Doris-BtL Fuels Flashcards

1
Q

What does BtL mean?

A

BtL = „Biomass to Liquid“ –> conversion of (solid) biomass to (liquid) fuels

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2
Q

What are the production pathways of BtL?

A
  1. Gasification of feedstock (biomass) 2. Fuel synthesis
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3
Q

Steps of gasification

A
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4
Q

What should be considered in the gasification process?

A

Targets for product gas

 Maximize energy yield

 Maximize share of CO, H2

 Minimize coke- and tar formation

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5
Q

What are the gasification parameters to take into consideration?

A
  1. Heat supply
  2. Gasification agent
  3. Pressure
  4. Reactor type

Note that the LHV of allothermal agents is higher than the autothermal agents

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6
Q

Gasification: What is the gasification product gas composition?

A

There are main an minor components:

Main components:

Fuel gases: CO, H2, CH4, hydrocarbons ( C2+)

Inert gases: N2, CO2, H2O

Minor, trace components

Tar: high-boiling (aromatic) hydrocarbons

–> condensation below ~300°C

Particles: ash, inorganics (K, Na, P)

N-compounds: NH3 , HCN

S-compounds: H2S, COS

Halogen com: HCl, HF

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7
Q

First step to use the gasification product gas?

A

We have to clean the gasification crude gases, because they have a lot of impurities, for fuel synthesis most of them need either little to no impuritites.

Crude gas cleaning: Usually a multi-stage procedure:

  1. Tar reducing gasification technologies
    e. g. multi-stage gasification
  2. Dry gas cleaning

–> Removal of particles by cyclones, electro filters, fabric filters, ceramic

filtes or sand-bed filters

–> Cleaning of hot gases possible

  1. Wet gas cleaning

„Washing“ of gas in washing towers using aqueous or organic solvents

–> Removal of particles and soluble compounds

–> Mature technology

–> Drawbacks: - no hot gas cleaning

  • recycling of washing liquids required
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8
Q

Gasification and fuel synthesis technologies have to be adopted to feedstock

For which feedstock gases is the fuel synthesis mature?

A

Mature technologies for processing of natural gas and coal are available

Technologies for processing of solid biomass is still R&D

Gasification of biobased feedstock (biomass)

Theory: wide varitety of biobased feedstock (agric. crops + wastes)

Reality: until now satisfying performance of biomass gasification only for wood (and straw) (–> benefits compared to use of wood for heat production?

Why?:

Problems at gasification of herbaceous crops and bio-wastes, e.g.

  • Long distance transportation for feedstock supply for large scale plants
  • low ash softening points
  • inhomogeneous feed materials
  • high amounts of impurities in product gases

–> feedstock pre-treatment (e.g. pyrolysis, torrefaction)

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9
Q

How is the gas quality for the following feedstocks?

  • Natural gas
  • Coal
  • Solid biomass
A
  • Natural gas –> H2 rich ( H2: CO ~2)
  • Coal–> H2 lean ( H2: CO ~1)
  • Solid biomass –> H2 lean ( H2: CO ~1,2)
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10
Q

What are the specific properties of solid biofuels?

A
  1. LHV of dry matter (MJ/kg)
  2. LHV (MJ/kg)
  3. Water content air-dry (%)
  4. Ash content (% DM)
  5. Softening point of ash (°C)
  6. Raw density (kg/cm³)
  7. Bulk density (kg/m³)
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11
Q

Torrefaction Biomass pre-treatment why?

A

–> Biomass becomes more coal-like

–> Improved processing by gasification

Technology

  • Mild pyrolysis (roasting) at 200 – 300°C without oxygen
  • Slow heating-up
  • Treatment time: 15 – 90 min
  • Directly or indirectly heated reactors (e.g. drum reactors)
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12
Q

What are the effects of torrification on solid biomass?

A

Effects on biomass

  • Drying, degassing and structural changes
  • Enhanced LHV:

LHV of crude biomass (wood, grass): 14 – 16 MJ/kg –> torrefied: 22 – 25 MJ/kg

  • Storability improved
  • Grinding faciliated –> for proper operation of circulating- bed and entrained-flow gasifiers
  • Pneumatic hauling faciliate –> for proper operation of circulating- bed and entrained-flow gasifiers
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13
Q

What are the Fisher Trops Fuels?

A

The Fischer–Tropsch process is a collection of chemical reactions that converts a mixture of carbon monoxide and hydrogen into liquid hydrocarbons. These reactions occur in the presence of certain metal catalysts, typically at temperatures of 150–300 °C (302–572 °F) and pressures of one to several tens of atmospheres. The process was first developed by Franz Fischer and Hans Tropsch at the Kaiser-Wilhelm-Institut für Kohlenforschung in Mülheim an der Ruhr, Germany, in 1925.

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14
Q

What are the products out of a Fischer–Tropsch process ?

A
  • C1-C4 – gases ~ 10 % (e.g. methane, propane, butane)
  • petrol/diesel-fraction ~30 – 40 %
  • waxes ~40 – 50 those can be further hydro cracked (with H2 hydrogen) and produce the other products
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15
Q

What are the properties of FT-diesel fuels?

A

Properties of FT-diesel fuels

  • Defined composition – adjustable to demands of engines
  • No aromatics
  • High cetan number (> 70)  lower fuel consumption ?
  • Reduced emissions compared to fossil diesel fuels (soot etc.)
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16
Q

Draw the whole FT process:

A
17
Q

Give an example of GtL, and how is it used in Germany?

A

Example of FT Synthesis with natural gas as a feedstock:

Shell mitteldestillate synthesis - Feedstock: Natural gas (
Shell GtL- plant

 Malaysia

 2 mio. litres/day)

GtL-Synthetic fuel blends, for example: “V-Power”, “Ultimate”

18
Q

What other BtL pathways are there?

A

Methanol MeOH- synthesis

19
Q

What can we do with Methanol?

A

Almos everything…

20
Q

How to compare the efficiency of different transportation fuels?

A

Efficiency formula!

21
Q

What are the synthesis pathways for Di-methyl-ether (DME)?

A
22
Q

Summarize BtL-fuels

A

SS17_I: Bioenergy Technology (13 decks)

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