Pressurisation Perils in Storage Silos

Silo over-pressurisation is a serious threat as it can result in pollution and could even put lives at risk. Companies in the cement industry face increasing demands to minimise their impact on the local environment, particularly with regard to odour and pollution, and the escape of powder materials from storage silos represents a significant risk. However, this is an avoidable issue if appropriate safety measures are put in place.

Using lime in cement production

Lime is a fundamental component in cement production due to its binding properties. During the cement manufacturing process, limestone is heated in a kiln at high temperatures (usually around 1450°C) in a process known as calcination. This process breaks down the calcium carbonate into calcium oxide (lime) and CO_2. The lime then reacts with silica, alumina, and iron oxide present in the raw materials to form clinker, the key intermediate product in cement manufacturing. When combined with water, lime forms calcium silicate hydrates, the primary compounds responsible for the strength and durability of cement. The proportion of lime in the cement mix is carefully controlled to achieve the desired properties, such as setting time, compressive strength, and workability.

Additionally, lime helps improve the overall chemical and physical characteristics of cement, enhancing its stability, resistance to sulfates and durability in various environmental conditions. Its availability and cost-effectiveness make lime an indispensable ingredient, contributing to the efficient and economical production of cement in the construction industry. The consequences of over-pressurisation

Over-pressurisation can lead to severe results, ranging from environmental pollution and equipment damage to potentially catastrophic silo ruptures. This risk is especially critical when dealing with corrosive materials like lime powder. When filters become clogged or delivery pressures exceed the filter’s capacity, air pressure can build up within the silo, causing dust and powder to escape into the atmosphere. Numerous cases have been documented where silo tops were covered with powder, pressure sensors were malfunctioning, and vent filters were blocked, rendering them ineffective. Unfortunately, there is a widespread misconception within the industry that the greatest risk to silos comes from overfilling, when, in fact, over-pressurisation is the main culprit.

Many operators, particularly in the cement industry, have been complacent about the dangers of silo over-pressurisation, accepting pressure blowouts as a normal occurrence and noting that ‘the pressure relief valve is doing its job.’ However, pressure relief valves (PRVs) are intended as a last line of defense; they should not be triggered under normal operating conditions. When PRVs are forced to release pressure, it signals a deeper problem that could compromise the integrity of the silo.

In the worst cases of neglected silo protection, pressure build-up can blow filter units from the silo roof, causing extensive damage and endangering the lives of workers below. The more common (but equally concerning) issue is product leakage by lime powder and other powder materials.

There is also a worrying trend of erecting scaffolding around silos and covering them with plastic sheets in an attempt to contain escaping powder. Such actions, while indicative of an awareness of the problem, do not address the root cause; ultimately, the situation will deteriorate further.

Understanding the causes of over-pressurisation

Over-pressurisation occurs when the volume of air entering the silo exceeds the amount that can escape. This can happen if the filters become clogged, or if tanker drivers apply more pressure than the silo can handle. While delivery tankers can withstand pressures up to 2 bar (29 psi), storage silos can rupture at as little as 1 – 2 psi above atmospheric pressure. Statistics produced by ENVEA show that poor driver behaviour is a significant contributor to over-pressurisation incidents, though this issue has been challenging to control.

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Read the article online at: https://www.worldcement.com/special-reports/25112024/pressurisation-perils-in-storage-silos/