Problem:
- hazard related to the possibility of explosive ammonia-air mixtures in a newly designed catalytic flue gas denitrification system using ammonia water
Solution:
- explosion risk assessment at the system design stage – review of flammable and explosive substances that may occur within the designed system, classification of explosion hazard zones, technical and organisational recommendations to ensure an adequate level of safety in the area of the designed system
ATEX analysis at the design stage of the flue gas denitrification system
The new investment project involving the construction of the flue gas denitrification system, which will be fitted in the coal-fired boilers of one of the power plants, in addition to performing design works, delivery and assembly of equipment and systems, required an ATEX analysis, and more precisely – explosion risk assessment. It was due to the use of ammonia solution in water (concentration of ammonia water 24% vol.) in the newly designed system.
The decision to commission an explosion risk assessment at the design stage indicates a professional approach to the project. With the document developed by our experts, technical solutions that will ensure a minimum level of safety can be taken into account. It often allows to eliminate a number of erroneous assumptions, and thus reduce the costs of modifications of the constructed system.
Course of the explosion risk assessment for the designed system
The ammonia water flue gas denitrification system will be used to reduce the concentration of nitrogen oxides (NOx) in the entire flue gas stream. The project foresees the use of SCR technology (Selective Catalytic Reduction) with the use of two catalytic converters. These converters will be located at the end of the process line, behind the flue gas dust extraction and desulphurisation systems.
The following areas of the flue gas denitrification system were included in the risk analysis and assessment:
- ammonia water unloading and storage plant,
- ammonia water distribution plant into converters,
- system for preparing and injecting ammonia water into the catalytic converters, including the converters.
The starting point for the explosion risk assessment was to determine the type of explosion hazard zones and their range. For this purpose, flammable and explosive substances that may occur within the designed system were reviewed. The 24% solution of ammonia water was verified. The possibility of gaseous release of ammonia from the solution under the influence of temperature (heating) was also taken into consideration.
In order to classify explosion hazard zones and assess the hazards within them, a technological description of the installation was necessary, together with guidelines for its operation. The mixture of ammonia and air will pose the main risk in the individual areas of the analysed flue gas denitrification system.
The calculations for explosion hazard zones were carried out in accordance with PN-EN 60079-10-1:2016: Explosive atmospheres. Part 10-1: Classification of areas – Explosive gas atmospheres, which indicates the calculation procedure for estimating the range of zones in the case of gases and vapours of liquids.
Recommendations resulting from the explosion risk assessment
The explosion risk assessment was carried out for normal, undisturbed operating conditions of the analysed system. Within the framework of the document, the experts included relevant recommendations concerning the operation of the system according to the classified explosion hazard zones. These recommendations apply to, among others, the course of maintenance and repair works in designated areas, inspecting the working condition of equipment operating in explosion hazard zones, as well as the adaptation of electrical equipment to the category required for particular zones.
The developed technical and organisational recommendations will allow to ensure an adequate level of explosion safety in the area of the designed system without incurring excessive costs.
