Is the string forming because the meal is sticky, or because the gas-meal flow is unstable? That distinction decides where the diagnosis goes next. Sticky meal means chemistry — chloride and alkali condensing at the wrong axial position, low melting-point compounds bridging across the cyclone cone. Unstable flow means temperature swings, kiln backend instability, or feed-rate moves the cyclone cannot absorb. Most strings in real plants come from both, and the stop frequency tracks whichever is dominant in the current campaign.
Why this matters in the preheater
Strings restrict gas flow through the cyclone and, when they grow large enough, pull cleaning crews into the tower at temperatures and locations that are increasingly unsafe. Each unscheduled string-clearing event costs production time, exposes maintenance staff to risk, and accelerates wear on refractory linings around the affected stage.
The chemistry side is the cheaper one to fix when caught early — bypass extraction, tighter chloride control on AFR, hot-meal monitoring — and the harder one to fix when it has been allowed to build for a campaign. Once the volatile cycle is established, every restart re-seeds the string. Frequent formation is a signal that the chemistry boundary needs attention, not just better cleaning intervals.