Kapitel – Miljøprojekt Nr. 1259 2008 – Reduktion af luftforurening fra gasmotoranlæg

Reduktion af luftforurening fra gasmotoranlæg

Summary and conclusions

Considerable emissions of unburned natural gas (UHC) come from the exhaust of gas engines. Most of the UHC is methane. The RECCAT system is a novel environmental facility that is able to incinerate the unburned UHC in the engine exhaust.

Preliminary financial estimates indicate that great advantages may be achieved by introducing facilities that reduce the emissions of UHC from gas engines in Denmark.

RECCAT ApS was supported by a grant from the Danish EPA under a subsidy scheme called “Virksomhedsordningen 2006”.

The purpose of the project is to demonstrate, study and prove in full-scale the ability of the RECCAT system to clean the flue gases from CHP plants for undesirable emissions of UHC, CO, formaldehydes (FA), and odour.

The main target group of RECCAT is CHP plants with natural-gas- (or biogas-) fired engines. The target group of the project is the Danish EPA and decision-makers who decide if new initiatives are to be taken to reduce emissions of CO2 equivalents.

The project involved the following:

Measurements of the reduction of UHC, CO, FA and odours at a CHP plant with the RECCAT system installed, and with small quantities of additional natural gas for the RECCAT system for optimization.
Establishment of a calculation method to estimate the optimal RECCAT reactors for future projects at CHP plants.
Estimation of typical costs of RECCAT installations at CHP plants, using results from this project and previous projects.

The project was carried out in cooperation with Rask Mølle Varmeværk (RMV), Danish Gas Technology Centre (DGC) and NIRAS. The measurements at RMV were carried out by DGC in cooperation with RECCAT, and NIRAS made the financial estimates. NIRAS also had primary responsibility for validating the results of the project.

The measurements were made in August/September 2007. The project was completed within the time schedule.

At the start of the measurements, the catalyst material in the reactors of the RECCAT system had been in operation for about 5400 hours.

The following conclusions can be drawn from the project:

The measured cleaning efficiency for UHC was between 73 and 98%.
The cleaning efficiency for CO was more than 99%.
The cleaning efficiency for formaldehyde was about 95%.
The cleaning efficiency for odours was between 58 and 85%.
Emissions of lubrication oil were reduced.
Taking all the measurements into account, cleaning efficiencies between 40 and 98% were found for UHC, dependent on the load and additional natural gas.
At RMV and 100% load, the smallest emissions of UHC occur with 2.9-3.0% additional natural gas.
The uncleaned exhaust emissions of UHC from the engine at RMV depend highly on the load.
To protect the catalyst material in the reactors, the temperature must be kept below 620°C.
The UHC cleaning efficiency of the reactors depends strongly on the maximum temperature and less on the load.
The reactors for new plants should be made 40% larger.
With the present kind of catalyst material the maximum?? temperature in the reactors should be above 600°C in new plants. This is achieved by making the reactors longer, which improves the heat exchange.
Permanent efficiency for UHC cleaning of more than 90% can be achieved with reactors 40% larger and by increasing the pellet size of the present catalyst material by 50% to reduce the back pressure of the system.
Formaldehyde is reduced to a very low level by the RECCAT system. Some formaldehyde is produced in the exhaust system of the engine.