High Free Lime in Clinker

Diagnostic approach

High free lime means lime (CaO) did not fully combine into the clinker silicate phases. Two questions drive the whole diagnosis, in order: is the result real, and is the cause chemistry or burning?

1. Confirm it’s real. Re-sample and re-run, and confirm the free-lime test method and sample prep. Sampling/prep/test error is a common and cheap-to-rule-out cause; do this before treating the value as a process change.
2. Separate chemistry from burning. Recompute LSF and Bogue phases from verified XRF. A high LSF or poor burnability (coarse silica) is a chemistry cause; adequate chemistry with high free lime points to burning (low burning-zone temperature, short retention/high feed, fuel/air or flame issues).
3. Read free lime with C3S and the burning picture. High free lime with low C3S is a classic under-burning or hard-to-burn signal (see Low C3S); interpret it alongside BZT, feed/fuel stability, and O2/CO.

Chemistry causes

• LSF too high. Higher LSF caps more potential C3S but is harder to burn; if burning can’t keep up, uncombined lime shows as free lime. Recompute LSF from verified oxides (see LSF, SM, AM) and check the limestone proportion/feeder and quarry variation.
• Poor burnability — coarse silica / high quartz. Coarse quartz resists combination, leaving free lime even at normal LSF. Check raw meal residue (90µm/212µm) and silica source.
• Raw mix variability / poor homogenization. Swings in raw meal chemistry or weak blending mean parts of the feed are over-limed; review chemistry standard deviation and silo/blending operation. See Raw Mix Design.

Burning / process causes

• Burning zone temperature too low. The most direct burning cause; review BZT (or a proxy) with the free-lime trend and kiln amps.
• Short retention time / high feed rate. Pushing production shortens time at temperature; check feed vs fuel and kiln speed.
• Fuel/air balance, flame shape, burner. Poor combustion (high CO, excess or deficient air), a long/lazy or unstable flame, or burner condition/position can under-burn the charge — observe O2/CO and flame per site procedure.
• Coating / ring / snowman / cooler effects. Rings and buildups disturb the thermal profile; poor cooler performance lowers secondary air temperature and the burning-zone heat. Look for these signatures in amps/temperature trends.

Sampling / testing issues

• Test or prep error. Wrong sampling point/time, inadequate grinding, or reagent/standardization problems shift the free-lime number. Confirm the method.
• XRF/XRD interpretation limits. Free lime should be a measured value (chemical titration or XRD). Bogue phases are potential, not measured (see Clinker Phases) — don’t infer free lime from Bogue.

Step-by-step diagnostic workflow

1. Verify the free lime result (re-sample/re-run) and confirm the test method.
2. Pull the free-lime trend and the matching C3S/strength trend.
3. Recompute LSF and Bogue from verified clinker XRF; check raw meal XRF and variability.
4. Check raw meal residue/fineness (burnability).
5. Assemble the burning picture: BZT or proxy, feed rate, fuel rate, kiln amps, O2/CO/NOx.
6. Look for recent changes: quarry/material, feed rate, fuel, burner work.
7. Rank the likely causes from the evidence; identify the single highest-value check.
8. Document findings and route to process engineering/QC — recommend checks, do not authorize changes.

Inputs needed

Verified free lime value and trend; target free-lime range; clinker XRF; raw meal XRF; LSF/SM/AM; Bogue phases (if available); kiln feed rate; burning-zone temperature or proxy; kiln amps; O2/CO/NOx; fuel rate and recent changes; raw meal residue/fineness; recent quarry/material/feed changes; sampling and test-method details.

Outputs expected

A ranked, evidence-linked list of probable causes; the specific checks or data that would confirm or rule out each; the single highest-value next check; a clear statement of which data is still missing; and an explicit reminder that any field change requires authorized personnel and site procedure.

AI agent diagnostic prompt

You are a cement kiln/quality advisor diagnosing HIGH FREE LIME in clinker. You are ADVISORY ONLY: you recommend checks and reasoning. You never authorize kiln setpoint, feeder, fuel/air, burner, or production-rate changes, product release/spec decisions, or environmental decisions — those require authorized personnel and site procedure.

STEP 1 — REQUEST MISSING DATA FIRST. Before ranking causes, ask the user for any of the following that are missing, and do not guess:
- Current free lime value and recent trend
- Target free lime range
- Clinker XRF (CaO, SiO2, Al2O3, Fe2O3, SO3, MgO, alkalis)
- Raw meal XRF
- LSF, SM, AM
- Bogue phases (if available)
- Kiln feed rate
- Burning zone temperature or a proxy
- Kiln amps / torque
- O2, CO, NOx
- Fuel rate and any recent fuel changes
- Raw meal residue / fineness
- Recent quarry / material / feed changes
- Sampling and free-lime test method details

STEP 2 — VERIFY THE SIGNAL. Ask whether the free lime result was confirmed (re-sample/re-run, method checked). If not, recommend verification before any process interpretation.

STEP 3 — SEPARATE CHEMISTRY FROM BURNING. Using the data: recompute/inspect LSF and burnability (residue, quartz) for chemistry causes; inspect BZT, feed/fuel, O2/CO, flame for burning causes. State which the evidence supports.

STEP 4 — RANK CAUSES. Give a ranked list (most to least likely) with, for each: the evidence for it and the single specific check or data point that would confirm or rule it out.

STEP 5 — NEXT CHECK + ESCALATION. Name the highest-value next check, list still-missing data, and state the escalation path (process engineer, QC manager; QC for any spec/soundness/release decision).

RULES:
- If key data is missing, say so and request it instead of fabricating a conclusion.
- Distinguish facts, assumptions, and recommendations.
- End with: "Advisory only. Confirm with the appropriate human authority and your plant's procedure before any change."