Environmental Engineering Reference
In-Depth Information
Off gas
Power
Steam
Liquids
Biomass
Pretreatment
Grinding
Drying
Gasification
Air, oxygen, steam,
or mix
Atmospheric or
pressurized
Direct/indirect
Gas cleaning
Gas processing
Reforming, CH
4
→
H
2
/CO
Shift, adjusting H
2
/CO ratio
CO
2
removal, reducing
amount of inert
Synthesis
Catalyst depends on fuel
Reactor: fixed bed or slurry
Reactions exothermic
“Wet,” cold
“Dry,” hot
→
process heat
Unconverted gas:
Gas turbine
→
power
Recycle loop
FIGURE 7.1
Overview of standard biomass gasification facility. The processes for “gas
processing” are optional. (Source: Adapted from Olofsson et al. (2005).)
using Fischer
Tropsch (FT) synthesis. The remaining unreacted syngas is used to pro-
duce electricity. Each unit in the process has a certain
function
to fulfill, effecting
changes from its inputs to outputs. All functions combined in the right order accom-
plish the overall change from feed to products. This process is used to illustrate the
concepts discussed in this chapter.
-
7.3 ANALYZING THE OUTSIDE OF A PROCESS
In general, the design of a process must always start by analyzing and specifying
how the process will be interacting with the outside world. Any process to convert
biomass to energy is part of a physical supply chain, both upstream and downstream.
Furthermore, it is also imbedded in a socioeconomic and natural environment
(see Figure 7.2).
At the
upstream side
of the supply chain, one faces the following issues. Who will
supply biomass to the process? What can be delivered in terms of annual amounts with
seasonal effects, variability in quality, security of supply, and expected price ranges?
Is the logistics of the biomass delivery feasible and what are feed storage requirements
at the site of the process? What source of oxygen to use for partial combustion (air,
oxygen, water)? Is cofiring with a second feedstock desirable?
At the
downstream side
, similar issues arise concerning the slate of energy pro-
ducts to be generated by the process. What annual amounts of energy (power, fuels,
and thermal heat) can be sold to (permanent) customers and at what quality speci-
fications? Is there a dynamic pattern in the product demand? What is the minimum
uptime (=hours per year a process is capable of producing) for securing supply
requirements of the customers? What are realistic past price ranges and future price
scenarios? In addition to making products, any process generates some waste and
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