Old power plants - new life with #pyrolysis pre-plant! (Part1)

Main problems

In the 1980s power plants are mostly designed as #coal fired #powerplants. The #incineration of #waste was not kept in mind because of large dumps with low fees.

Old incineration technology

A really old style power plant has normally a quite simple flue gas cleaning, means mostly a simple bag filter, in some cases a single washer system. So after 30 years of operation and restictivly changed emission limits this plant seems only ready for shut down... (Simplified ...)

Fixed to one input material

Conventional power plants are designed for one type of input material and the used grate was specialized to this fuel. An old power plant uses mostly a "dirty, but cheap fuel", but this fuel requires do to actual standards a large flue gas cleaning system to reach the actual emission limits.

In the past the standard input material was often coal/lignite, but in the actual discussions about CO2 this fuel is not longer welcome and all operators of coal fired power plants have acceptance problems...

Experiences of alternative plants

Following experiences are important for discussion and possiblible solution:

Burgau waste pyrolysis plant "MPA Burgau" (1982 - 2015)

Burgau plant was a combined plant with rotary kiln drum and a burning chamber with boiler island. In this case the pyrolysis process (inside of the oxygen free kiln drum) was independent of the incineration process (inside a standard burning chamber. With some additives it was quite simple to fix chlorine and sulphur into the pyrolysis coke. As a result the pyrolysis gas and the following incineration was much cleaner and a BiCar injection with a bag filter reached the actual and future(!) emission limits.

Due to the mixed waste input the pyrolysis coke had a high content of heavy metals and also due to the process a high content of TIC. This causes problems in the dumping of the coke, but this was still a #CO2-minus technology!

Hamm RDF pyrolysis plant "Contherm" (2001 - 2009)

A much modern concept was an independent operated pre-plant for an existing coal power plant. The kiln drum was heated by natural gas systems with high-tech recuperation systems.

So end of the day with 29.2 GJ/h natural gas and 240.7 GJ/h RDF you could produce 232.8 GJ/h pyrolysis gas which was substituted coal in the coal power plant. Additionally the pyrolysis coke was treated and delivered 28.3 GJ/h on top.

With an energy ratio of 1:9 you can produce pyrolysis gas for an older coal power plant! By the way you are solving the #plastic #waste problem.

Sorting technology

In the 2010th the sorting technology is "ready for operation". With the modern sorting possibilities a plastic waste stream can be checked for (heavy) metal content and sort them out. This new possibilities should causing much cleaner pyrolysis coke!

Heating requirements

For plastic / RDF pyrolysis you need a process temperature of appr. 500 °C. The net energy for the decomposition can be roughly calculated with 400 kWh per ton. This take results of the choice of technology.

In case for more details please check my LinkedIn-article about kiln temperatures.

Flue gas heated kiln

After kiln heating you will have an offgas with appr. 600 °C. Depending of the possible flue gas temperature you will have a thermal energy requirement of 1,200 kWh (900°C) to 800 kWh (1,200 °C) per ton dry input.

Additionally you need electric power for the fan(s), but main expensive disadvantage is the changing of the existing boiler and its parameters. But don't forget the dust in the flue gas...

Natural gas heated kiln

To operate with a nearly untouched power plant you can operate the kiln drum with natural gas burners. Gas burners can operate up to 1,700 °C. So you need below 600 kWh gas energy per ton input.

With good recuperation systems the efficiency can be increased and will be reducing the off gas temperature, too. But you need still additional electric power for the burner and recuperation fans.

Electric heated kiln

Electric heated kilns have the best thermal energy efficiency (nearly 100 %) because of no flue gas losses, no fans and no flue gas emissions.

They are still ready and also high efficient for future high temperature processing, ex.g. #hydrogen production from bio waste.

In combination with a wind power plant or a PV you can add a really green pre-plant to your existing infrastructure.

Conclusio

With a rotary kiln pre-plant you can still operate your well-known power plant, but due to the kiln process possibilities your emission parameters will be much better!

With a good designed rotary kiln system you are also variable in different feed stocks and different processes from torrefication - pyrolysis - thermolysis - gasification.

Interested in a consulting meeting and/or basic study to check out your local possibilities?