19/11/2024
Gasification Projects: Why they fail
This short thought is written upon request and to help ASP Cleantech come up with a strategic plan that will enable the company withstand headwinds that might come
up in future. The thought is based on the author’s own experience and information that has been reported in the open literature.
A gasification reactor can be at the center of a plant that produces different kinds of products such as liquid fuels (Fischer Tropsch and many other plants such as in the
Mobile Process). Gasification plants can also be at the center of projects that produce syngas for electrical power production or for the recovery of hydrogen as is the case
with the Cleantech project.
The failure of a gasification plant should therefore be linked to the application. Many failed gasification plants are linked to the Fischer Tropsch (FT) synthesis process
for the production of petrol and diesel. The problem here is that the cobalt/iron catalyst used sometimes cannot withstand the high temperature of the process, so
that any improperly designed FT reactor that cannot quickly remove heat as it is produced quickly results in catalyst deactivation and loss of stability. But this
application doesn’t concern us.
There are also secondary installations upstream and downstream of a gasification reactor for feedstock pretreatment and for the cleaning and conditioning of the
synthesis gas for downstream application, irrespective of the nature of the application. These installations eat up 50 % of total capital outlay in gasification
applications broadly speaking.
For our purposes we won’t need any upstream secondary installation that is linked to drying given that our feedstock has about 1 % moisture content. However, we
have to reduce feedstock size to less than 100 microns otherwise the performance of the gasifier reactor will drop in parameters such as overall syngas yield and calorific
value. Not probably dealing with this could be a source of problem. In particular, the feedstock size and type will determine what gasifier design is appropriate. Failure to
link design of gasifier to your feedstock type and size could also be a problem.
Once the gasifier design has been selected the next challenge will be how to deal with tar. But a good design should mean that tar production has been reduced to
levels that would not present a problem to downstream syngas consumption equipment. It is important to know for our purposes what level of tar will work for
PSA systems, and/or electrolysis. This will then be information to be relayed to gasifier designers such that tar production is reduced by as much as possible.
Reducing tar and particulate and solid contents of syngas as it leaves the gasifier will drastically reduce downstream cleaning and conditioning units, keeping plants
viable economically. The best way to achieve this is to get a gasifier design capable of in-situ tar reduction to further reduce the cost of cleanup if plasma gasification is
not an option for initial cost reasons. This requires a catalyst that can withstand the high gasification temperature for many months before reactivation. If this cannot be
achieved at some point and the cleanup system is not ready for large tar concentrations because the catalyst deactivated, the plant can fail.
Sometimes dry-cleaning instead of wet-cleaning is more efficient especially if downstream application is operating at the temperature of the gasifier. This is
unlikely going to be the case for our application as both PSA and electrolysis are low-temperature systems, requiring wet-cleaning (to lower syngas temperature), and
some inherent water-related environmental concerns. Issues like this also have to be taken into account at the stage of gasifier design. For example, how will you treat
the large volume of water generated because your syngas was bubbled into a water tank or vessel to remove impurities? Over time this water will need treatment as
required by the law. A good gasifier system will increase syngas yield and minimize the release of tar and other impurities. If wet cleaning of the syngas is employed very
little polluted water will be generated.
As a matter of strategy it is recommended to get units that have been designed and tested for long either at a pilot or commercial scale. Relying on laboratory untested
technologies (across the board) can lead to failure.
The last but not the least is the lack of a regular source of feedstock to ensure that the plant runs continuously. What will happen if you suddenly don’t have a reliable
source of feedstock? Some gasifiers have failed for this simple reason. Hence a versatile gasifier capable of gasifying multiple feedstocks will be a good insurance
for this type of problem. A plan for the identification and acquisition of the various types of feedstock has to be part and parcel of a successful project to provide flexibility. Lack of feedstock can result from competition in the industry, or from a change in government policy on municipal waste management.
ASP Cleantech is taking all these factors into account to ensure a long-term operation of its integrated waste-to-syngas, syngas cleaning, hydrogen separation and
synergistic methanol production systems.
Eliasu A. Teiseh
Research & Development Manager, PhD