Challenges of Plant Decommissioning

By Paulo Siqueira

Many of us have already experienced the satisfaction of participating in a new project and the construction of new plants. This is a great experience. However, like any other man-made structure, explosives plants also have a limited life span and will reach the end of their operational life and eventually require a decommissioning. There are several reasons for this to occur: outdated technology, low performance. high maintenance cost, environmental issues, safety concerns, etc. As such, it is important for plant owners to plan for the eventual decommissioning of these facilities.

Decommissioning an explosives plant can be a challenging task.

From handling hazardous materials, dismantling contaminated equipment and disposing hazardous waste, the process requires careful and detailed planning, execution, and management to ensure compliance with company’s safety and environment standards.

Despite the challenge, in this article we will explore one such success story, where an explosives plant was decommissioned in a way to reduce environmental impact and provide safety for all workers involved. We will look at the strategies and techniques used to achieve this outcome. Ultimately, this case study provides valuable insights into how to approach the complex task of decommissioning a chemical plant, and highlights the importance of careful planning, collaboration, and attention to detail in ensuring a successful result.

For more than a decade, Nitrosul's packaged emulsions plant in Minas Gerais - Brazil was in operation but since the manufacturing site was acquired by Austin Powder Brasil it was decided to close down the plant permanently for not meeting the current explosive Basis of Safety (BOS) standards and Good Explosives Practices and build a new plant following more modern and safe technologies.

The plant was designed and built in 2010 with in-house resources and produces around 6,000 ton/year of packaged emulsion in two shifts.

Decommissioning works were started and completed safely in 2022. There were no injuries whatsoever and no unexpected incidents occurred during the decontamination, disassembly and removal of the equipment and hazardous waste disposal. All the work was carried out by the Austin Powder Brasil team, which resulted in better control and keeping safety standards high, as well as low cost for decontamination and dismantling.

The plant in its last days of operation.

A key aspect of conducting safely such type of operation is having a well-developed and sound implemented Safety, Health & Environment Management System with a set of standards and procedures to assist all personnel to meet the company’s requirements, the current industry practices, and regulatory requirements.

The following are the management elements that were applied during the work:

1) Decommissioning of Redundant Assets:

A detailed decommissioning work plan was prepared three months in advance considering the most important aspects for the work:

• A decommissioning manager was appointed to be responsible for the project.
• The scope of the project was clearly defined.
• The history of the plant was reviewed with the previous owner/designer.
• List of chemicals/products handled in the plant and PPEs required.
• A complete inventory of equipment.
• Definition of the decontamination method.
• Disassembly sequence.
• Disposal of equipment and hazardous waste.
• Applicable references, procedures and good practice standards have been identified.
• The work schedule has been established and agreed.
• The work team was defined.

2) Basis of Safety.

An overview of BOS was done to refresh the knowledge concerning the hazards involved wit: matrix emulsion, ammonium nitrate solution and prill, gassing solution (sodium nitrite) and emulsifier.
Aiming to mitigate an undesirable event with the risk of propagation to the neighboring plants, Bulk Emulsion (left) and ANFO (right) the performance of hot works would only be carried out when these two plants were not in operation.

3) Hazard Identification, Risk Assessment & Control:

A hazard study was carried out to identify any hazards which could arise or represent potential for incidents. The scope of HS considered:
• The hazards and risks associated with dismantling contaminated plant equipment.
• The impact and interference of the work on neighboring plants, bulk emulsion and ANFO.
All findings – hazards and respective control measures – were communicated to all workers involved in the operation.

4) Standard Operating Procedure (SOP):

An SOP wasdeveloped to support the PTW system, considering that this work had special aspects and would be performed for the first time on the site. So, the SOP helped the operators to perform their tasks efficiently following a clear step-by-step instruction and providing an on-the-ground approach to ensure that the job would be completed as planned AND in case of any deviation by unexpected situation that could compromise safety, they should stop the work promptly. This proved to be the correct attitude when they stopped working as soon as they found emulsion inside the hollow base pad of the cartridging machine before using the pneumatic hammer to break the concrete floor and remove the equipment.

5) Training:

Considering that decontamination and disassembly operations can only be carried out by competent people, specific training was given to the operators, mechanic & electrician and safety technician involved in the service, including: the SOP; inherent dangers and respective protective measures; SDS - Safety Data Sheets for each product handled in the plant and use of PPEs required in this type of work.
Thus, the team members were appointed, trained, and retrained to ensure they understood and have the necessary knowledge to fulfill the task.

6) Permit to Work (PTW).

The PTW system was widely used in all instances, ensuring that the nature of the work is clearly defined, responsible persons identified, hazards and suitable controls specified, and the equipment removed in a safe manner with adequate communication throughout the process with all those involved in the work (SAFEX). PTW were issued for:

• Hot work.
• Lifting weights while removing equipment.
• Working at height ?
• Isolation of plant for hazardous substances; the plant is isolated by physical disconnection from all lines of AN Solution, gassing solution and emulsifier. All non-essential energy sources were also disconnected - electrical and pneumatic.
• Equipment to be decontaminated/burned.

7) Decontamination of Building and Equipment:

The decontamination method followed the experience acquired by the company and the SAFEX Good Practice Guide - GPG 09/01 Decontamination of Equipment Prior to Maintenance.
Decontamination of emulsion is difficult because of the high-water resistance. As there was no steam available on the site, the equipment was washed with pressurized hot water. To complete decontamination, it was required the use of a detergent to break the emulsion structure.

The hidden hazards: The false white plastic wall installed at the back of the plant, between the cartridging machines and the matrix emulsion buffer tank while improving the visual appearance of the plant also hid the danger of contamination. Probably the emulsion leaked on the upper floor where the buffer tank was placed flowed and accumulated between the masonry wall and the plastic wall.

When the “fake” white plastic wall was removed, emulsion residues that had accumulated were identified.

Before and After: removing waste emulsion in the drainage system.

PC Emulsion pump: disassembly, decontamination and removal.

The floor had to be broken up to remove the reactor and the cartridging machines.

Emulsion Reactor: the most critical part of the operation was removing the emulsion reactor. The need for hot work to remove the platform around the reactor required a high degree of cleaning and decontamination of the equipment. The task was carried out safely as planned.

• Washing: a complete washing of the walls, access platform, support structure and emulsion reactor (inside and outside) was carried out. Contaminated thermal insulation was soaked thoroughly. Everything was washed and rewashed several times before being considered safe to undergo the hot work required for platform cutting.
• Removing thermal insulation: when removing the aluminum layer that contained the thermal insulation, the AN contamination was observed and removed. The reactor was washed several times and after no longer showing signs of contamination, it was taken to the burning ground.
• Preparing for burn: a wooden bed was prepared, and wood was also placed inside the reactor.
• After burn: the burning took place safely and effectively. The day after the burning, when the reactor was cooled, the equipment was examined by the plant supervisor and responsible for the burning ground - and considered decontaminated for not showing any evidence of contamination by AN and emulsion.

Equipment subjected to burning: all process equipment with potential for hidden contamination were burned in the burning ground and this included: ANS lines, jacketed lines, mixers, reactor and valves. Equipment and piping where emulsion and ANSOL could be trapped inside of hollow sections/cavities and it was not possible to visually ensure that the decontamination was effective, such as: welded tubes, pipes, mixer, valves, and shafts, were subjected to burning.

Burning potentially contaminated equipment can result in detonations. Therefore, procedures for the safe operation of the burning ground must be followed in addition to the task being performed by a trained and experienced worker.

All equipment considered completely clean and decontaminated were identified with a tag a “decontamination certificate” containing a unique number, attached to all equipment leaving the plant.

8. Hazardous Waste Disposal. Basically, two types of waste generated had to be properly treated: contaminated wastewater and hazardous solid waste.

Wastewater: contaminated water generated when washing equipment and the building was collected in reservoirs, analyzed by the laboratory and later sent to a company specialized in treating this type of effluent.
Solid waste: the solid waste characterized by emulsion and ammonium nitrate was collected and destroyed in the burning ground. Contaminated thermal insulation, which cannot be set on fire or could be destroyed internally, was also sent to a specialized landfill licensed to receive hazardous waste.

9. Emergency Response Plan:

An emergency plan has been prepared based on the emergency scenarios identified during the hazard study;

• Risks inherent in hot work and fire propagation
• Risks inherent in lifting and moving heavy loads
• Use of high-pressure machine with hot water
• Interference of work in the operation of neighboring plants – ANFO and Bulk Emulsion.
  Actions were developed and operators were trained to control/mitigate the consequences of these undesirable events.
  The works were carried out as planned and, as there were no surprises, the ERP did not need to be activated. However, it was ready to be put into practice if necessary.

End of work

After weeks of careful planning and management the work was accomplished safely and effectively. The operation involved a team of trained workers supported by management who worked diligently to identify potential hazards always present in explosives manufacturing sites. Their attention to detail and proactive approach to safety measures ensured that all equipment was decontaminated, removed and the hazardous waste properly disposed.

The successful conclusion of this challenging work not only demonstrates the importance of safety management system but also serves as testament to the effectiveness of proper planning and discipline in following of safety protocols and good explosives practices.

References:

• Austin Powder SHES Manual Part 15 - Decommissioning of Redundant Assets
• Austin Powder Explosives BOS Principles, 2nd Edition
• SAFEX Good Explosives Practice Guide GPG 09(01): Decontamination of Equipment Prior to Maintenance