Can You Handle Alternatives?

As far back as the 1970s, cement plants in Europe and the US were blending traditional fossil fuels with shredded tyres and waste from timber production. Indeed, the cement sector was one of the first to explore waste feedstocks as effective alternatives to coal and pet coke.

Recently, with fuel accounting for a rising percentage of cement clinker production costs, more and more producers have sought to secure suitable waste streams – for use both as fuel and in their raw feed mix – to achieve cost-effective production that is also recognised as being more sustainable.

Indeed, a handful of cement plants around the globe are able to boast 100% alternative fuels (AFs), raising the bar for the sector and challenging fossil fuel-reliant plants to look to locally available wastes as fuel sources – from non-recyclable plastics, commercial mixed wastes, and shredded upholstery to biomass like rice husks, sugar cane bagasse, and pelletised animal meal.

Physical properties and productivity

The choice of AFs requires careful consideration as the implications for productivity and process design can be significant. One of the major differences between solid fossil fuels and waste-derived alternatives is the way they flow through the process, typically determined by their physical properties and moisture content.

Efficient and continuous material flow is a critical element of dry-process cement manufacture, so any accumulation or blockages can choke productivity and profitability. Hang-ups in storage systems and build-ups in chutes and process vessels can cause serious obstructions that impede equipment performance and reduce efficiency.

Material build-up can occur in many places in the plant, and in several forms. Accumulation often occurs in riser ducts, feed pipes, cyclones, transfer chutes, and storage bins, as well as kilns and coolers. In extreme cases, massive buildups can suddenly break loose and suffocate the process, potentially causing significant damage to equipment and almost invariably prompting the need for unscheduled downtime.

It is worth stating that buildups of AF materials can happen even in well-designed systems. Changes in process conditions, the raw materials themselves or even the weather can have an effect on material flow, and a small amount of accumulation can quickly grow into a serious blockage, with obstructions often leading to secondary problems.

Accumulations of some AFs are even susceptible to spontaneous combustion, while others may accelerate wear, tear, and corrosion of structures, and deterioration of conveyor components. A preventive approach to controlling buildups and blockages is the only way to address these issues and prevent unscheduled downtime.

Safety risks resulting from build-ups

Lost production is usually the primary cost of flow problems, but the expense can become apparent in a variety of secondary ways. Shutdowns to clear blockages and buildup also cost valuable process time and maintenance hours. That increases maintenance costs and diverts service teams away from core activities, potentially introducing needless safety risks.

Refractory walls can become worn or damaged by tools or cleaning techniques. When access is difficult, removing material blockages may also introduce serious risks for personnel. Working platforms are usually needed to reach access points, and there is a risk of exposure to hot debris, dust, or gases when chunks of material stuck to the sides of a silo, hopper, or bin are suddenly released. If the discharge door is in the open position, material can suddenly evacuate, causing unsecured workers to get caught in the flow. Cleaning vessels containing combustible dust – without proper testing, ventilation, and safety measures – could even result in a deadly explosion with as little as a spark from a shovel.

Many of the most common problem areas for accumulation are also classified as confined spaces, requiring a special permit for workers to enter. The consequences for untrained or inexperienced staff can be serious, including physical injury, burial, and asphyxiation.

Enjoyed what you've read so far? Read the full article and the rest of the April issue of World Cement by registering today for free!

Read the article online at: https://www.worldcement.com/special-reports/11042025/can-you-handle-alternatives/