1.
Plant and process description.
Outline. Our system generates electrical energy using municipal solid waste
(MSW) as fuel. Waste is converted into a working gas called synthesis gas
(syngas) via plasma gasification, which is, in turn, used to run a diesel generator
capable of producing up to 1.5 MW of continuous power.
The ce25 consists of 3 main components: the reactor, gas cleaner and diesel
generator. (Please refer to Figures 1 and 2 for diagram and process flowchart
respectively)
a. Reactor. This component consists of the following sections:
i. Dryer column. As the feedstock is fed at the top, it is initially dried
using the hot gas from the engine exhaust. This allows the system to
process MSW with up to 50% moisture content without significant
loss of reactor efficiency.
ii. Reaction chamber. As the waste passes the dryer section it enters the
main reactor, where three plasma torches heat the feedstock up to
900 C, completely breaking it down into pyrolisys gas, consisting
mostly of charcoal, tar vapor and gases such as CO, CO2, H2 and
water. By controlling the access of oxygen and using a proprietary
recirculation system, these gases are reduced to CO, CO2 and H2.
iii. Fly ash is collected at the bottom of the reactor where it can be easily
extracted.
b. Gas cleaner. The working gas is passed through a cooling water column as
well as a series of filters in order to prevent tars, dust and other particulates
from entering the engine. Furthermore, it is quenched rapidly (~1500 °C/s)
to avoid the formation of PCB’s and chlorinated dioxins/furans. An alkaline
solution is used in the wash water to neutralize potential acid formation in
the recirculation system.
c. Genset. Syngas exits the gas cleaner at roughly 80 °C and is pulled into the
engine air intake via a proprietary gas manifold where it is mixed with air.
The syngas/air mixture is burned in the engine replacing the diesel, therefore
reducing fuel consumption by up to 90%.
i. Flare. The reactor will begin producing syngas when the operational
temperature exceeds 400° C, however, this syngas is relatively dirty
and could be detrimental to the engine’s lifetime. It is recommended
that while the reactor reaches its operational temperature, the syngas
be burned off, therefore, the ce25 has a built in propane flare that
should be run for the first 30 minutes.
2.
Basis of Design:
a. Planned throughput: The ce25 is designed to process approximately 1 ton of
municipal solid waste per hour, however, this number will depend on
variations in feedstock, and most notably, water content. A higher
percentage of moisture implies longer dwell times of waste in the reactor,
since much of the heat will go into evaporating the excess water instead of
gasifying solids.
b. Planned output (material & energy): [Material] From the total feedstock
mass, 80-90% will be converted into working gas; a remaining 10-15% will
be active carbon (char) and 1-5% fly ash. A small amount of tar has been
observed to mix with condensed water at the bottom of the reactor. This
byproduct can be re-injected into the reactor for breakdown. [Energy]
Typical syngas caloric values are ~7MJ/kg. This allows the ce25 to produce
up to 1.5 MW of electricity via a diesel generator.
c. Operating parameters (temperature, pressure, etc.). As feedstock enters the
machine, it passes a pre-heating phase in the dryer column at 300 °C. As it
enters the main reactor, the plasma torches break down the waste at a
working temperature of 900° C; the gas is circulated within the reactor
between 600° and 900° C. As the gas leaves the reactor at temperatures of
~500° C, it enters the gas cleaner where it is quenched, cooling the gas down
to ~80° C, the temperature at which the syngas enters the diesel engine. Note
that our system works in a closed cycle, therefore, the syngas burned in the
engine and expelled in the exhaust at temperatures exceeding 600°C is
pumped back into the reactor in the dryer column.
The overall pressure in the reactor vessel as well as the gas cleaner is
slightly below atmosphere (~500 mbar).
d. Planned uptime and planned downtime. The system is designed to run 23
hours per day, with a scheduled downtime of 1 hour for cleaning. This is
mostly due to char buildup, which although necessary for the gasification
process, can exceed a certain thickness that impedes adequate gas flow. The
torch electrodes have an average lifetime of 1000 hours; replacement takes
30 minutes.
e. Planned operations and maintenance budget.
???
3.
Process Flow Diagrams (PFDs).
a.
4.
See Figure 2.
Piping and Instrumentation Diagrams (P&IDs).
a. See attached.
5.
Major equipment specifications.
a. Not sure what goes here. Should we attach genset/conveyor specs?
7.
Plant production and operating records including:
a.
Material input.
b.
Material output.
c.
Energy output (gross and net).
d.
Plant availability.
e.
Operating history.
f.
Any material testing data.
g.
Any emissions testing data.
h.
Actual operations and maintenance costs.
Figure 1. ce25 diagram showing main components.
Figure 2. ce25 flowchart showing main processes and byproducts.