A unique explosion protection installation designed by us for an international food additives manufacturer combines explosion prevention and isolation in line with ATEX standards. This system not only safeguards the cellulose grinding process but also ensures uninterrupted plant operation—while reducing the project’s total cost.
The Challenge
- Processing (including grinding) cellulose carries high fire and explosion risks.
- Frequent activations of the explosion suppression and isolation system generated costs.
- The client wanted to modify the existing explosion protection system to reduce costs while maintaining the highest level of plant safety.
- Installation could only be carried out during a scheduled one-day production shutdown.
Solution
- We designed a coherent explosion protection system that reduced risk to a level acceptable to the client.
- Our concept included solutions unavailable from competitors.
- The proposed system reduced the total cost of ownership (TCO) by 35%.
- The client decided to implement the same “Shrek” mill protection system in other plants across Europe.
Our client is an international group specializing in food additives — primarily cellulose fibers. Their products are key ingredients in items like yogurt, and they operate facilities in several European markets. At this scale, process continuity is crucial — but the product itself makes things complicated.
Cellulose: A Subtle But Serious Explosion Risk
Cellulose is highly flammable and explosive. On the six-level combustibility scale (BZ1–BZ6), cellulose ranks at BZ5 and ignites at just 340°C. Its minimum ignition energy (MIE) is only 30–100 mJ—enough to be triggered by a small electrostatic discharge.
A cellulose dust explosion can damage buildings, injure people (e.g. lung injuries), or even be fatal. Its explosion severity (Kst) ranges from 50 to 150 [bar·m/s], and its maximum explosion pressure reaches 11.5 bar. This makes process safety absolutely critical during cellulose processing.
Grinding Cellulose: Where the Danger Lies
Cellulose arrives at the facility in briquettes, which are fed into a mill. There, it’s ground into fine dust for pneumatic transport. The dust is conveyed to a mechanical separator (cyclone), then collected and packaged. The finest dust escapes the cyclone and moves through ducts into a baghouse filter.
At every stage, dust is present—and under unfavorable conditions, it can ignite and explode. Even a human-generated electrostatic discharge (10–30 mJ) can ignite cellulose dust.
Urgent Need to Optimize the HRD System
The grinding and dust collection process was protected by a highly effective HRD (High Discharge Rate) suppression and isolation system. Sensors inside the equipment detect early explosion signs — pressure or flame — and trigger suppressant bottles in milliseconds. The extinguishing agent is released into the system, halting the explosion at its source, while decoupling valves block propagation.
Due to cellulose’s explosiveness, however, the HRD system was frequently triggered — causing costly downtimes. Every production delay risked major contract losses, prompting the client to seek a cost-effective solution that didn’t compromise safety.
How We Convinced the Client to Invest in Ex Safety
Our safety experts conducted in-depth analyses and worked directly with the client’s management to understand the full context. We then proposed an innovative concept — not the cheapest option, but compelling due to its long-term value.
Our solution — unavailable from competitors — cut project and maintenance costs significantly. It also improved protection against secondary explosions, safeguarding people, equipment, and ensuring ATEX compliance.
New Approach to Cellulose Mill Explosion Protection
Grinding poses serious explosion risks due to airborne dust clouds. One frequent cause of mill explosions is foreign objects sucked in with raw material or air intakes, sparking during turbulent motion inside the mill.
While the mill was already protected by HRD, it had three unsecured air inlets — two for the mill and one for the pneumatic system. During an explosion, fire and pressure could escape through these channels, causing dangerous secondary explosions.
To address this, we proposed installing IsoDisc isolation valves on each inlet.
IsoDisc is a passive mechanical isolation valve. Under normal conditions, airflow keeps the valve plate open. In an explosion, rising pressure instantly closes the valve, isolating the system and stopping the spread of fire and pressure. The solution complies with EN15089.
The solution earned the nickname “Shrek,” as the IsoDisc valves on the inlets resemble the cartoon ogre!
Protecting the Pneumatic Transport System
As process safety experts, we focus not only on preventing explosive atmospheres but also on eliminating ignition sources.
In this case, smoldering cellulose particles from the grinding process were the main concern, as they could trigger the HRD system when entering downstream equipment. To prevent this, we proposed an Atexon spark detection and extinguishing system on the transport pipe.
Atexon uses an infrared sensor to detect sparks or hot particles and instantly activates extinguishing. It adapts to the particle type and quantity—without disrupting production. (See our similar project for a tea dedusting system.)
We also designed backdraft dampers for air ducts between the cyclone and filter, protecting the pneumatic system from explosion blowback—often more damaging than the initial blast.
Imperial Sugar Explosion: A Lesson in Secondary Explosions
The 2008 explosion at Imperial Sugar in Port Wentworth, Georgia remains a tragic example of inadequate explosion protection. Fourteen people died and dozens were injured due to secondary dust explosions in unprotected, high-risk areas.
Photos from the aftermath show the devastating scale of destruction. The tragedy highlights the importance of proper Ex zone risk assessment and comprehensive protection systems—especially where organic dust is present.
Source: Associated Press
How to Optimize Explosion Protection Costs
When designing explosion protection systems, we consider more than just compliance with ATEX requirements. We also evaluate total costs—not only purchase and installation, but lifecycle costs (Total Cost of Ownership, TCO).
To calculate TCO, you must include:
- Purchase and installation of components and system startup
- Annual maintenance costs
- System restoration costs after activation
To optimize spending, we proposed a fully compliant and low-maintenance protection system.
Two Options for Mill Protection Under ATEX:
- System 1: 5 HRD bottles (2 existing + 3 new)
- System 2: 3 IsoDiscs + 2 existing HRD bottles
Full HRD protection of the air inlets would require 3 additional bottles. Without them, explosion suppressant could escape. By contrast, System 2 isolates the inlets with IsoDiscs, reducing required suppressant.
Assuming equal installation and inspection costs, the key TCO difference lies in post-activation restoration:
- System 1: 5 components require recharging
- System 2: Only 2 need servicing
HRD vs IsoDisc:
If the cost to restore one component = X, then System 2 (with IsoDiscs) reduces total cost by approximately 35%.
How IsoDisc Reduced Total Cost of Ownership
- It’s a reusable mechanical solution with no post-activation servicing.
- It enhances the HRD system’s effectiveness, retaining suppressant within the mill and improving efficiency with fewer bottles.
Precise Planning = Rapid Installation
We completed all modifications—including dedusting system upgrades—during a single scheduled shutdown. Working closely with maintenance and production teams, we carefully planned each step to minimize operational disruption.
Our team operated strictly within designated areas, securing all sensitive equipment from contamination or damage. We upheld rigorous safety standards, aware that even a brief pause in Ex environments threatens production continuity. After installation, the site was cleaned and returned to full operation immediately.
“Shrek” Succeeded in Poland—and Belgium
Grinding cellulose is like taming a dragon—high risk, high stakes. But as our client’s case shows, smart engineering can reduce risk and cost simultaneously. We helped the client:
- Significantly reduce explosion risk
- Protect human life and company assets
- Minimize unnecessary system activations
Success in Poland led to a twin “Shrek” installation in Belgium. We hope to support the client’s future explosion safety investments across Europe, the US, Canada, and Australia.
ATEX Safety in the Food Industry: We Know It Inside Out
At GRUPA WOLFF, we understand the challenges of food production facilities. For one major sugar producer, we designed a comprehensive explosion protection system fulfilling 22 recommendations from their Explosion Protection Document (EPD).
With extensive experience in both new facilities and modernization projects, we focus on ensuring process continuity in Ex zones and eliminating ignition risks where flammable dusts like cellulose are processed.
Our explosion protection solutions comply with ATEX, while also being optimized for TCO and ease of maintenance.
Our engineers regularly conduct explosion safety audits, identifying hazards and recommending optimal worker protection measures.
Need a reliable partner to secure your food production line—on time and on budget?
Get in touch—our experts will help you improve explosion safety and secure funding for ATEX protections.