Fives Pillard: Complete Technical Guide

Fives Pillard is one of the most respected names in industrial combustion, and for cement engineers the name is inseparable from the rotary kiln burner. For more than a century the company has designed, manufactured and commissioned firing systems for the cement industry, from the classic single-channel kiln burner of the early twentieth century to the modern low-NOx, high-momentum, multifuel burners that today fire the largest precalciner kilns in the world. This article is a complete technical study of Fives Pillard burner technology as applied in cement plants: it explains how a modern kiln burner is constructed, how the aerodynamics of the flame are engineered, how fuel is prepared and transported to the burner, how alternative fuels are handled, and how the burner interacts with the kiln system, the refractory lining and the clinker quality. It is written for process engineers, production managers, maintenance teams and graduate engineers who want to understand the burner not as an isolated piece of hardware but as the central instrument of the clinkering process. The article covers burner selection, installation, operation, tuning, troubleshooting and optimization, and it closes with a series of practical recommendations that can be applied in any plant that relies on a rotary kiln fired by a Fives Pillard system.

The Role of the Kiln Burner in the Cement Process

The rotary kiln is the heart of a cement plant, and the burner is the instrument that delivers the energy that drives clinker formation. Clinker is produced when raw meal, preheated and partially calcined, is subjected to temperatures in excess of 1400°C in the burning zone of the kiln. That temperature field is created almost entirely by the flame produced by the kiln burner, and the characteristics of that flame determine everything downstream: the rate of heat transfer to the charge, the temperature profile along the kiln, the formation and survival of the coating, the thermal load on the refractory, the volatilization of alkalis and sulfates, and the final clinker quality. A burner that produces a short, intense flame will create a hot, localized zone that melts the charge surface, while a long, lazy flame may not reach the required sintering temperature at all. The Fives Pillard philosophy is built on the idea that the flame must be engineered to match the process: flame length, flame shape, momentum, swirl and mixing must all be adjusted to the kiln diameter, the fuel quality, the feed rate and the production target.

The burner also has a profound influence on thermal efficiency. In a modern dry-process kiln, the flame gas temperature at the nose of the flame can reach 1800–2000°C, and the radiative heat transfer from the flame and the surrounding coating is what completes the clinkering reaction. A well-designed burner promotes early ignition of the fuel, complete combustion within a controlled zone, and minimal excess air. Each percentage point of excess oxygen in the kiln exit gas costs fuel, and each percentage point of combustible loss in the clinker or the dust stream represents energy that was paid for but never used. Fives Pillard burners are designed to operate with total combustion air requirements close to the stoichiometric value while still achieving complete burnout, which is one of the reasons they are specified by plants that are serious about specific heat consumption.

Finally, the burner is the principal tool for managing the process environment. The shape and position of the flame influence the formation of the coating on the refractory, which protects the bricks from thermal shock and chemical attack. The burner also controls the thermal NOx generation at the flame, the oxidation of sulfur compounds, and the release of volatile components from the charge. In short, the kiln burner is not just a fuel delivery nozzle; it is the most powerful process control instrument available to the kiln operator after the kiln speed and the feed rate. Understanding the Fives Pillard burner means understanding how to use that instrument to its full potential.

Company Heritage and the Evolution of Fives Pillard

Fives Pillard has its origins in the French industrial engineering group Fives, combined with the combustion specialist Pillard, which was founded in Marseille and became known worldwide for oil and gas burners in industrial furnaces. Over the decades the brand accumulated an exceptional body of knowledge in combustion engineering, burner aerodynamics and fuel handling. When Fives acquired the combustion activities, the combined company inherited thousands of burner installations across the cement, minerals, sugar, aluminum and energy industries. In the cement industry specifically, Fives Pillard became known for the Rotaflam line of rotary kiln burners, which are now installed on kilns with diameters ranging from 3.0 m to over 6.0 m and production capacities from a few hundred tonnes per day up to more than 12,000 tpd in the largest plants.

The technical evolution of the kiln burner mirrors the evolution of the cement process itself. The first rotary kiln burners were simple pipes that blew pulverized coal into the kiln at the discharge end. As kilns grew larger and production rates increased, burner manufacturers added primary air fans, swirl vanes and adjustable nozzles to shape the flame. The oil crises of the 1970s pushed the industry toward coal and petcoke, which required burners with much higher momentum to entrain the hot secondary air and stabilize the flame. The 1980s and 1990s brought the first multichannel burners, in which the fuel is delivered through a central channel and the primary air is split between an axial channel, a swirl channel and a radial channel, each of which can be adjusted independently. Fives Pillard refined this concept into the Rotaflam, adding swirl impeller systems and a dedicated fuel channel design that permits very high substitution rates of alternative fuels without loss of flame stability.

Today, Fives Pillard continues to develop the technology in three directions: lower emissions, higher alternative fuel rates, and digitalization. Low-NOx burner geometries reduce the formation of thermal NOx at the flame front, which allows plants to meet tightening emission limits without expensive post-combustion treatment. High alternative fuel capability is delivered by burner designs that accept coarse particles, plastics, biomass, sewage sludge pellets, tyres and other wastes, injecting them through dedicated channels with sufficient momentum to burn them in flight. Digitalization is delivered through burner monitoring systems that measure flame temperature, flame shape and fuel distribution in real time, giving operators the data needed to tune the burner continuously. This article explains all of these developments in detail, starting from first principles.

Fundamentals of Combustion in a Rotary Kiln

Combustion of a solid or liquid fuel in a rotary kiln is a highly complex process that involves several overlapping physical and chemical phenomena: drying of the fuel particles, devolatilization or vaporization, mixing of the fuel vapor with oxygen, ignition, homogeneous gas-phase combustion, and heterogeneous combustion of the residual char. For pulverized coal, the sequence begins when the coal particles enter the hot zone of the flame and are heated to the devolatilization temperature of roughly 350–450°C. The volatile matter, which may represent 25–40% of the coal by mass, is released as a cloud of hydrocarbons around each particle and burns rapidly in the gas phase, generating the bright yellow flame that is characteristic of the kiln burner. The remaining char particle then burns more slowly by surface oxidation, a process that takes much longer than the volatile combustion and requires oxygen to diffuse to the particle surface.

The overall rate of combustion is controlled by the slowest step. In the early part of the flame, the rate is controlled by the rate of volatile release and by the mixing of volatiles with oxygen; in the latter part, it is controlled by the rate of oxygen diffusion to the char surface and by the temperature of the particles. This has an important consequence for burner design: the flame cannot be shortened simply by increasing the temperature, because the char burnout is limited by mixing. What the burner must do is promote turbulent mixing between the fuel jet and the surrounding air while at the same time creating a region of recirculation near the burner tip that anchors the flame and stabilizes ignition. The Fives Pillard design achieves this through a combination of high jet velocity and adjustable swirl, which creates a central recirculation zone that draws hot combustion products back toward the burner tip and continuously ignites the incoming fuel.

Stoichiometry is the other fundamental parameter. The stoichiometric air requirement of a typical cement coal is approximately 8.5 to 9.5 kg of air per kg of fuel, depending on the composition. The air that participates in combustion in the kiln comes from two sources: the primary air carried by the burner itself, which represents typically 8–15% of the total, and the secondary air that enters the kiln from the clinker cooler, which provides the remaining 85–92%. The secondary air is hot, at 800–1100°C in a well-run plant, and its sensible heat contributes significantly to the flame temperature. The momentum of the primary air must be sufficient to entrain this large mass of hot secondary air into the flame; if the primary air momentum is too low, the flame becomes lazy and the secondary air bypasses the flame, cooling the kiln gases instead of feeding the combustion.

Burner Design Principles: Momentum, Swirl and Flame Shape

Every modern kiln burner is a compromise between conflicting requirements, and the Fives Pillard Rotaflam is no exception. The central design parameters are the jet momentum, the swirl intensity, the number of air channels, and the distribution of primary air between those channels. The jet momentum, defined as the product of the primary air mass flow and its velocity, determines the ability of the burner to entrain secondary air and thus controls the flame length and the recirculation pattern. High momentum produces a short, intense flame with a well-defined mixing region; low momentum produces a long, soft flame. The swirl intensity, defined as the ratio of tangential to axial momentum, determines the degree of rotation in the air jet. Swirl creates a radial pressure gradient that generates the central recirculation zone, accelerates mixing near the burner tip, and widens the flame. A burner with high swirl and low axial momentum produces a wide, short flame; one with low swirl and high axial momentum produces a narrow, long flame.

The Rotaflam burner family is built around a fuel channel and an annular primary air system that is divided into three independently adjustable sections: axial air, swirl air and radial air. The axial air exits through a series of straight nozzles arranged around the fuel channel and contributes the forward momentum of the jet. The swirl air exits through tangential slots that impart rotation to the flow. The radial air exits through small holes arranged radially near the burner tip and creates a ring of turbulence at the nozzle exit that stabilizes ignition. By adjusting the pressure and flow to each of these three sections, the operator can shape the flame continuously over a wide range: from a short, wide, intense flame suitable for low-alkali clinker and a heavy coating to a long, narrow flame suitable for hard-burned clinker and fragile refractory. This flexibility is the defining feature of the third-generation multichannel burner and the reason Fives Pillard burners can be tuned to almost any kiln and any fuel. The role of each channel of the Rotaflam burner is summarized in the table below, which is the reference that operators use when making deliberate adjustments:

Channel	Function	Effect when increased	Typical share of primary air
Axial air	Forward momentum of the jet	Longer, narrower flame; deeper heat penetration	65–80%
Swirl air	Tangential rotation, central recirculation	Shorter, wider, hotter flame; stronger ignition anchor	10–25%
Radial air	Ring turbulence at the nozzle exit	Stabilizes ignition, strengthens early mixing	5–15%
Fuel channel	Carries pulverized fuel in transport air	Higher fuel rate raises the kiln thermal input	Transport air 2–4%
Cooling jacket	Protects the burner tip from radiation	Extends the tip life; small air cost	1–3%

In practical terms, the burner settings are expressed as the distribution of primary air, typically 70–85% axial, 10–25% swirl and 5–15% radial, with the exact split chosen to match the operating target. A typical starting point for a coal-fired kiln is 70–75% axial air with a primary air ratio of 10–12% of stoichiometric. If the flame is too long and the burning zone is weak, the operator increases the swirl air and reduces the axial air, which shortens the flame and raises the peak temperature. If the coating is too heavy or the refractory in the burning zone is overheating, the operator does the opposite, lengthening the flame and spreading the heat over a larger shell area. The skill of the kiln operator lies in reading the process signals, the kiln shell temperatures, the NOx level, the clinker quality and the f-CaO, and translating them into burner adjustments.

The Rotaflam Multichannel Burner Architecture

The Rotaflam burner is a concentric assembly of pipes and nozzles that can be dismantled for maintenance. At the center is the fuel channel, which carries the primary fuel, normally pulverized coal or petcoke, entrained in a transport air stream. Around the fuel channel is the first annular space, which carries the swirl air through tangential vanes positioned at the burner tip. Around that is the second annular space for the axial air, which exits through a ring of axial nozzles, and outside that is the radial air ring. The outermost part of the burner is the cooling air jacket, which protects the burner tip from the radiative heat of the flame; the tip is one of the hottest parts of the whole kiln system and is normally made of heat-resistant cast steel or a ceramic-metal composite. The burner is mounted on a carriage with horizontal and vertical adjustment mechanisms, so that the position of the burner nose relative to the kiln axis can be set precisely, and it slides through the kiln hood into the nose ring area.

For alternative fuels, the Rotaflam offers a variety of supplementary channels. Solid alternative fuels such as plastic flakes, granulated tyres, biomass and RDF are injected through a separate annular channel or through a central tube that passes inside the main fuel channel, depending on the required momentum and the particle size. Because large particles require a long residence time to burn completely, the injection velocity for alternative solids must be chosen carefully: too high a velocity and the particles fly through the kiln and fall into the clinker; too low and they drop immediately onto the charge near the nose. Liquid alternative fuels, including waste solvents and used oils, are atomized by a dedicated lance with a spray nozzle, and gaseous fuels such as natural gas or hydrogen-rich gas can be delivered through a central gas lance. A fully equipped Rotaflam can therefore burn coal, petcoke, gas, oil, and several alternative fuels simultaneously, each through its own controlled channel, which gives the plant enormous fuel flexibility.

Instrumentation completes the burner. A modern Fives Pillard installation includes flow and pressure transmitters on every air channel, fuel flow metering, and often a flame monitoring camera that looks into the kiln through the burner pipe or a separate sight port. The control system records the primary air ratio, the channel pressures and the fuel split, and it can be interfaced with the plant DCS so that the burner settings are logged together with the kiln parameters. Some installations include an optical pyrometer sighted on the burning zone that measures the flame and shell temperatures, allowing the operator to correlate burner settings with the thermal condition of the kiln. This instrumentation is the foundation of burner optimization, because nothing can be optimized that cannot be measured.

Primary Air Systems and Fans

The primary air for a kiln burner is supplied by one or more dedicated fans, sized to deliver the required mass flow at the required pressure. The primary air fan of a Rotaflam installation is typically a high-pressure centrifugal fan with a design pressure of 350–600 mbar and a flow corresponding to 8–15% of the stoichiometric combustion air. The air may be heated or cold; in most plants it is cold ambient air, which has the advantage of simplicity, while some plants heat it with a small heat exchanger to improve flame temperature. The fan discharge is split into the three channel legs by a distribution manifold with butterfly or iris valves, each leg equipped with an orifice plate or venturi and a pressure transmitter for flow measurement. The control philosophy is to maintain a constant primary air ratio across the load range, which means the fan damper or variable speed drive responds to the fuel flow so that the primary air rate follows the kiln throughput.

The design of the air split is critical. The swirl leg usually operates at the highest pressure drop, because the tangential vanes are deliberately restrictive to create the desired swirl intensity. The axial leg operates at a lower pressure drop through straight nozzles, and the radial leg through the smallest orifices. The pressure signals from each leg are used for tuning: when the operator changes the setting of a leg valve, the pressure in that leg changes, and the flame shape changes accordingly. Because the legs interact, tuning is an iterative process: the operator changes one setting, observes the effect on the flame and on the kiln, then compensates for the interaction with the other legs. Fives Pillard supplies tuning charts and commissioning services that map the burner behavior over the whole operating envelope, so that the plant has a reference table linking valve positions to flame characteristics.

The air that transports the pulverized coal to the burner is a separate system. The coal feed system, normally a loss-in-weight feeder or a volumetric feeder with a rotary airlock, delivers a metered flow of coal to the transport air stream, which is generated by a roots blower or a centrifugal fan. The transport air velocity in the coal line is maintained between 18 and 25 m/s to keep the coal in suspension, and the pressure at the burner is monitored to detect blockages, pipe wear or feeder problems. The amount of transport air is significant, typically 2–4% of stoichiometric air, and it must be added to the primary air when calculating the true primary air ratio. Modern installations include a transport air flow meter in the DCS and often a coal flow meter that measures the solids concentration in the line, which allows a very precise control of the fuel energy input to the kiln.

Fuel Preparation for the Burner

The quality of the flame starts in the fuel preparation plant, and no burner can compensate for badly prepared fuel. For pulverized coal, the two critical parameters are fineness and moisture. The fineness of the coal is expressed as the percentage retained on a 90 micron sieve, typically 1–3% for coal and 2–5% for petcoke in a kiln application, plus the percentage on a 212 micron sieve, typically below 0.5%. Coarse particles burn slowly and may leave the kiln as cinders, increasing the heat consumption and damaging the clinker quality. The moisture of the coal as delivered to the burner should be in the range 1–2% for a flame that ignites promptly; higher moisture delays ignition, extends the flame and increases the risk of flame instability. The coal mill, whether it is a ball mill or a vertical roller mill, must therefore be operated with the hot gas temperature and the classifier speed set to deliver the required fineness at the required throughput.

Petcoke, which is increasingly common because of its low price, is more difficult to burn than coal because of its low volatile content, typically 8–14%, and its low reactivity. Petcoke requires finer grinding, usually 1–2% residue on 90 micron, and it requires a burner flame that provides a longer residence time in the high-temperature zone. The Fives Pillard burners handle petcoke with a higher primary air momentum and a higher swirl setting to create strong recirculation, which keeps the char particles in the hot zone longer. Some plants blend petcoke with coal to improve ignitability, and the blend must be kept homogeneous in the silo to avoid combustion variations. The burner settings for a petcoke blend are usually re-optimized for each blend ratio, which underlines the importance of the flexibility of the multichannel burner.

Alternative fuels place even greater demands on the fuel preparation and injection system. Solid alternative fuels must be shredded to a controlled particle size, typically below 50 mm for most wastes and below 10 mm for high-grade RDF, dried to a moisture content that does not quench the flame, and fed through a system of rotary valves and screw conveyors that prevents both jamming and false air ingress. The calorific value of alternative fuels varies within and between batches, so the plant must have a robust blending and quality control scheme, usually based on X-ray or NIR analyzers, to keep the energy input stable. Because the particle size and density of alternative fuels differ from coal, they are injected through the dedicated channels with velocities tuned to their settling characteristics. Fives Pillard provides full engineering for the alternative fuel feeding line, including the safety systems, explosion protection and fire detection required by modern regulations.

Flame Characteristics and Their Effect on the Kiln

The flame in a rotary kiln has a structure that can be described in zones. Immediately at the burner tip there is an ignition zone, where the fuel is heated, devolatilized and ignited, aided by the recirculation of hot gas. This zone is short, typically less than 1 m, and its position is stabilized by the radial air and the central recirculation. Downstream is the main combustion zone, where the bulk of the fuel burns and where the flame reaches its maximum temperature; for a coal flame the peak gas temperature is 1800–2000°C, reached 2–6 m from the burner tip depending on the burner settings. Beyond that is the burnout zone, where the last char particles are consumed and where the gas begins to cool as it transfers heat to the charge and the lining. The total flame length in a modern kiln is typically 8–18 m, roughly 8–12 times the kiln diameter, with the exact value controlled by the burner settings.

The temperature profile of the flame has a direct effect on clinker quality. The burning zone is the region where the charge is maintained above 1400°C long enough for the clinker phases to form: alite (C3S) must nucleate and grow, and the liquid phase must be present in sufficient quantity to complete the reaction. If the flame is short and hot, the peak temperature is high and the reaction is fast, but the hot spot may be too narrow, leaving part of the charge underburned. If the flame is long and cool, the whole burning zone may sit below the clinkering temperature, producing a soft-burned, high-f-CaO clinker. The operator balances these effects using the burner, choosing the flame shape that gives the target f-CaO at the lowest possible heat consumption. In practice, a flame that is slightly longer than the theoretical minimum gives the best combination of low heat consumption and stable coating, because it spreads the thermal load over a larger area of brick.

The flame also controls the atmosphere inside the kiln. Near the burner tip the gas is locally oxygen-rich; downstream the oxygen is consumed and the gas becomes progressively more reducing if the fuel is in excess. A reducing atmosphere in the burning zone is always undesirable: it decomposes the C3S, it causes the formation of f-CaO, it discolors the clinker and it promotes the volatilization of sulfur, which then circulates in the kiln and causes build-ups. The operator therefore maintains a small margin of excess oxygen in the kiln exit gas, typically 1.5–3.5%, which ensures that the flame is fully oxidizing throughout its length. The flame shape and the excess air interact: a well-mixed short flame can burn with less excess air than a lazy long flame, which is one of the economic arguments for a high-momentum burner. The NOx level is another indicator: thermal NOx is formed at the flame front, so a change in NOx after a burner adjustment confirms that the flame temperature distribution has changed.

NOx Formation and Low-NOx Burner Design

Nitrogen oxides are formed in the kiln flame by three mechanisms: thermal NOx, which is produced by the reaction of nitrogen with oxygen at temperatures above roughly 1300–1400°C; fuel NOx, which is produced by the oxidation of nitrogen compounds in the fuel; and prompt NOx, which is produced by the reaction of hydrocarbon radicals with nitrogen early in the flame. In a rotary kiln with a short, hot flame, thermal NOx dominates, and the rate of formation increases exponentially with temperature. A burner that produces a flame peak of 2000°C will generate substantially more NOx than one that peaks at 1850°C. The NOx concentration in the kiln exit gas of a modern plant is typically in the range 300–900 mg/Nm3 as NO2, and many plants are now required to meet limits of 200–500 mg/Nm3, which demands both process measures and burner design measures.

The low-NOx design of the Fives Pillard Rotaflam is based on two principles: staged combustion and flame temperature control. Staged combustion means that the fuel is not all burned in the same stoichiometric zone. By injecting part of the fuel through a dedicated channel with a different air ratio, or by delaying the mixing of some of the primary air, the burner creates a fuel-rich zone early in the flame where the oxygen is insufficient for complete combustion. In that zone the nitrogen chemistry is driven toward molecular nitrogen rather than NO, and the heat release is spread over a longer distance, lowering the peak temperature. The second principle is simply to avoid unnecessary flame peaks by using a longer, softer flame where the clinker quality permits. Many plants find that a modest lengthening of the flame, achieved by reducing the swirl and increasing the axial air, reduces NOx by 20–40% with little or no effect on clinker quality.

Process measures complement the burner design. The primary method is the use of a low-NOx calciner, which burns 55–65% of the total fuel at a moderate temperature, typically 850–900°C, where thermal NOx formation is negligible; this alone reduces the kiln system NOx by a large fraction compared with firing all fuel at the kiln flame. The secondary measure is the control of the secondary air temperature and the kiln excess oxygen, both of which affect the flame temperature. Some plants add a selective non-catalytic reduction (SNCR) system using urea or ammonia injected at the preheater, which typically achieves an additional 30–60% reduction. The combination of a low-NOx burner, a low-NOx calciner and SNCR allows modern plants to meet the strictest European and North American limits. Fives Pillard engineers routinely perform burner tuning campaigns in which the NOx response to each burner parameter is measured, producing an operating map that balances NOx, heat consumption and clinker quality.

Alternative Fuel Firing at the Kiln Burner

The substitution of fossil fuels by alternative fuels is one of the most important economic and environmental levers available to a cement plant, and the burner is the component that determines how high the substitution rate can go. Alternative fuels fall into three broad classes: solid wastes such as RDF, SRF, plastic flakes, tyres, biomass and sewage sludge; liquid wastes such as solvents, oils and sludges; and gaseous fuels such as natural gas, landfill gas and hydrogen. Each class has its own combustion characteristics and its own injection requirements, and a Fives Pillard burner can be configured to handle them all, either alone or in combination. The key constraints are the particle size and the burnout time of the fuel, the stability of the flame with the changed heat release pattern, and the safety of the handling system.

The burnout of an alternative fuel particle in the kiln is governed by the particle size, the volatile content, the ash content and the temperature history of the particle. A 20 mm plastic flake devolatilizes quickly but leaves little char; a 30 mm tyre chip burns slowly and may require more than 10 seconds, which is comparable to the residence time of the gas in the kiln, so the particle must be injected with enough velocity to remain suspended and hot. Fives Pillard addresses this by injecting solid alternative fuels through a channel with a high jet velocity, typically 40–80 m/s, which keeps the particles in the flame region and increases their residence time. The injection point and the angle of the channel are chosen so that the particles pass through the hottest part of the flame, and the swirl air is adjusted to sweep them upward and prolong their path. In extreme cases, coarse fuels are fired at the calciner or through a separate chute into the kiln, which gives an even longer residence time.

High substitution rates change the economics of the plant dramatically. With thermal substitution rates of 60–90%, the fuel cost per tonne of clinker can be reduced by 40–60%, and the plant also benefits from the gate fees received for treating the waste. However, the risks must be managed: the variability of the fuel quality requires a flexible feed system and continuous quality monitoring; the volatile components of the waste, especially chlorine and alkalis, can create kiln blockages and refractory problems; and the changed flame shape can affect the coating and the clinker quality. The solution is a systematic approach: fuel characterization, feed system design, burner tuning and process monitoring, all of which are part of the engineering services that Fives Pillard provides with its burner installations. Plants that adopt this approach are routinely achieving substitution rates above 70% with a single kiln burner, and some have reached 90% or more on a sustained basis.

Burner Positioning and Kiln Geometry

The position of the burner relative to the kiln axis is a process parameter that is often undervalued. The burner must be centered on the kiln axis, both horizontally and vertically, so that the flame is coaxial with the kiln and the thermal load is symmetric around the shell. A burner that is off-center produces an asymmetric flame, with consequences that include hot spots on one side of the refractory, uneven coating, and premature brick failure. The vertical position is equally important: a burner that is too low directs the flame into the charge, causing local melting and coating instability; a burner that is too high directs the flame above the charge, wasting heat and failing to protect the lining with a coating in the lower quadrant. The recommended practice is to set the burner axis exactly on the kiln centerline and to re-check the alignment whenever the kiln alignment itself is checked, because both are subject to thermal and mechanical drift.

The axial position of the burner nose, that is, how far the burner tip projects into the kiln, is set during commissioning and is a compromise. A burner tip that projects far into the kiln is closer to the charge and gives a hotter nose region, but it is more exposed to radiation and wear, and it reduces the free area for the secondary air. A tip that is retracted keeps the burner cooler but lengthens the distance to the charge and may weaken the flame near the nose ring. The typical projection is such that the nose of the burner is flush with or slightly inside the kiln inlet flange, and the flame develops from there. The Rotaflam carriage allows the whole burner to be moved axially by a small range, and the optimum position is found by observation of the flame, the shell temperatures and the coating profile during commissioning.

The kiln hood and the nose ring area deserve special attention because they are the interface between the burner and the kiln. The hood must be sealed so that false air ingress is minimal, since false air entering at the hood bypasses the flame and increases the excess air without contributing to combustion. The nose ring, which protects the end of the shell, is usually lined with castables or precast segments, and its condition must be monitored because a damaged nose ring disturbs the secondary air flow and the flame stability. The sight port for the flame camera and the burner opening are on the hood, and the burner sleeve through which the burner slides must be sealed with a flexible gland. Good practice includes a weekly visual inspection of the hood, the nose ring and the burner tip, with a formal inspection every time the kiln is stopped.

Burner Tuning Methodology

Burner tuning is the systematic adjustment of the burner parameters to achieve a defined objective, and it should be a planned activity rather than an improvised reaction to process upsets. The Fives Pillard methodology starts with the definition of the objective, which is usually expressed in terms of three conflicting targets: minimum specific heat consumption, target clinker quality (f-CaO, free lime and alite content), and acceptable emissions, especially NOx. The secondary objectives include a stable coating, a refractory life above the design value, and a stable kiln operation with minimal instability. The tuning campaign begins with a baseline measurement: the kiln is operated at steady state, the burner parameters are recorded, and the process data are collected over several hours, including the kiln exit gas analysis, the shell temperature scans, the clinker quality data and the production rate.

The tuning itself proceeds in small steps. One parameter is changed at a time, by an increment large enough to produce a measurable effect, and the process is allowed to stabilize before the next change. The usual sequence is: first the primary air ratio, then the swirl-to-axial split, then the radial air, and finally the flame position. At each step the operator records the effect on the flame, the kiln exit temperature, the NOx, the f-CaO and the coating. The result of the campaign is a matrix of burner settings and their effects, from which the best operating point for each production mode can be chosen. It is important that the tuning is done with the fuel quality at its normal value, because the burner response to the settings depends on the fuel: a coal with a high volatile content responds differently to the swirl setting than a low-volatile petcoke.

Continuous optimization is a different activity from commissioning tuning. In day-to-day operation, the operator uses the burner as a control instrument: a slight change in the swirl pressure to raise or lower the burning zone temperature, an adjustment of the radial air to correct a coating instability, a change in the primary air ratio to compensate for a change in the secondary air temperature. These adjustments are small, are made deliberately and are recorded. The danger is the opposite behavior: operators who leave the burner untouched for months, or who adjust it at random in response to every alarm, both of which waste the capability of the instrument. The best practice is a daily burner log, a weekly review of the burner performance against the reference matrix, and a full tuning campaign whenever the fuel type, the fuel quality or the production target changes significantly.

Burner Maintenance and Component Life

The burner tip is the highest-wear component of the entire firing system. It is exposed to the full radiation of the flame, to the impingement of the fuel particles and to the thermal cycling of every kiln stop and start. In a typical coal-fired kiln the tip has a service life of 12 to 24 months, and in a kiln firing abrasive alternative fuels the life can be shorter. The Rotaflam tip is a replaceable component, made of a heat-resistant alloy or a ceramic composite, and it is designed so that it can be exchanged during a normal kiln maintenance stop without removing the whole burner. The maintenance procedure includes a dimensional check of the tip, a visual inspection for erosion and cracking, and a measurement of the nozzle diameters, because the erosion of the nozzles changes the air split and therefore the flame shape. Plants should keep a spare tip in stock, pre-drilled to the standard configuration, so that an unplanned replacement does not delay a kiln restart.

The air channels and the fuel channel are subject to internal erosion by the fuel particles, and the condition of the channel linings should be checked at every maintenance stop. The fuel channel in particular, through which the coal passes at high velocity, is usually lined with a wear-resistant material, and its internal diameter must be verified because an enlarged channel reduces the transport velocity and can lead to coal settling and blockages. The swirl vanes and the axial nozzles are machined components whose geometry defines the burner performance; they must be cleaned of deposits and their dimensions verified against the reference drawing. All bolts and fasteners in the burner head must be re-torqued after each re-assembly, and the head-to-body seal must be renewed, because a leaking seal destroys the calibration of the channel flows.

The routine maintenance program covers the whole firing system. The primary air fan is serviced according to its manufacturer’s schedule, including bearing lubrication and damper operation checks. The air distribution valves are inspected for free movement and their position transmitters are calibrated. The transport air blowers, the rotary feeders and the coal valves of the fuel system are checked for wear, and the explosion protection devices of the fuel lines, including the flap valves, are function-tested. The flame camera lens is cleaned and its cooling air flow is verified. Finally, the burner management system, including the flame scanner, the trip logic and the interlocks, is functionally tested: in a modern plant the flame scanner and the burner interlocks are part of the safety system, and a failed interlock test means the kiln must not be fired until the issue is corrected. A complete firing system audit, including a burner pull-out and dimensional inspection, is recommended every two to three years or after 20,000 hours of operation.

Troubleshooting Common Burner and Flame Problems

The most common burner-related problems in a cement kiln are flame instability, delayed ignition, an overlong flame, an overheated burning zone, and asymmetric burning, and each has a characteristic set of causes and remedies. Flame instability, seen as flickering, pulsation or frequent flame-outs, is usually caused by insufficient primary air momentum, a clogged channel, poor fuel quality or a large variation in the fuel feed rate. The first check is the fuel flow stability and the transport air pressure; the second is the channel pressures, which indicate partial blockages; the third is the fuel quality, especially moisture and fineness. If all are normal, the remedy is an increase in the primary air ratio or the swirl, which strengthens the recirculation and anchors the flame.

Delayed ignition, in which the flame develops far from the burner tip, is caused by fuel that is too moist or too coarse, by a low flame temperature or by excessive axial momentum that blows the ignition point downstream. The remedy is to improve the fuel preparation, reduce the axial air, increase the swirl and check the secondary air temperature, which should be above 750–800°C for stable ignition. An overlong flame, which shows up as a long warm zone and a cold kiln exit, is tuned by increasing the swirl and reducing the axial air; if this does not help, the primary air ratio should be reduced or the fuel fineness improved. An overheated burning zone, which appears as high shell temperatures and a heavy coating melt, is tuned in the opposite direction: more axial, less swirl, and a slight retraction of the burner nose.

Asymmetric burning, which causes a circumferential hot spot on the shell, is most often a positioning problem: the burner is off-center, or the kiln shell has sagged locally, or the nose ring is damaged and is deflecting the secondary air. The burner alignment must be checked first, then the shell ovality and alignment at the supports, and finally the nose ring condition. If the asymmetry persists with a centered burner, the cause may be a partial blockage of the swirl vanes on one side, which must be inspected during the next maintenance stop. Each of these problems has one thing in common: it is diagnosed from the process data, the shell temperatures and the flame image, and it is confirmed by the burner instrumentation. A plant that keeps its burner instrumentation calibrated and its operating logs accurate will find that most firing problems can be diagnosed in minutes rather than in days.

Commissioning a Fives Pillard Burner Installation

The commissioning of a new or rebuilt burner installation follows a disciplined sequence. The mechanical phase includes the installation of the burner carriage and its alignment to the kiln axis, the connection of the air and fuel lines, the calibration of the flow instruments, and the functional testing of the interlocks and the flame scanner. The cold commissioning phase verifies the air distribution: each leg of the primary air system is pressurized, its flow is measured at several damper positions, and the resulting flow curves are recorded as the reference for the operation. The fuel system is tested with air only, to verify the transport velocity and the absence of leaks, and the alternative fuel lines are purged and pressure-tested. Only then is the plant ready for the hot commissioning, which starts with the heating of the kiln and the first ignition.

The first ignition is performed with a pilot burner or a high-energy spark igniter, with the main fuel flow introduced gradually. The flame is brought up from a small, stable flame to the full operating flame over several hours, with the primary air ratio held at a conservative value and the swirl set for maximum stability. During the initial production period, the burner is operated at the recommended reference settings while the process data are collected, and the tuning campaign begins only after the kiln has reached steady state at the target production rate. The commissioning team observes the flame, records the burner parameters, and takes samples of clinker for quality analysis, and it uses the tuning methodology described above to find the optimum settings for the plant’s fuel and its production objectives. The final deliverable of the commissioning is the operating manual of the burner, which records the reference settings, the tuning matrix, the troubleshooting guide and the maintenance schedule.

The value of a professional commissioning extends far beyond the startup week. The reference settings established during commissioning become the benchmark against which all later operating changes are measured, and the tuning matrix becomes the training material for the plant’s operators and engineers. Plants that skip the systematic commissioning of their burners typically pay for it in higher heat consumption, more NOx, shorter refractory life and more frequent production upsets. Fives Pillard therefore emphasizes that the burner is delivered not as hardware alone but as a system that includes the engineering, the commissioning and the training, and it is this system approach that makes the difference between a burner that works and a burner that works optimally.

Case Study: Optimizing a Kiln Fired with Petcoke and RDF

Consider a typical application: a 4.6 m diameter kiln producing 5200 tpd of clinker, fired with a Fives Pillard Rotaflam burner, with a fuel mix of 70% petcoke and 30% RDF on a thermal basis. The plant’s objectives were to increase the thermal substitution rate to 50%, to reduce the NOx from 700 to below 450 mg/Nm3, and to hold the specific heat consumption at 3300 kJ/kg of clinker or better. The baseline audit showed that the flame was too short and intense, the NOx was high, and the RDF substitution was limited to 30% because coarse particles were falling out of the flame and ending up in the clinker. The shell temperature scan showed a hot zone centered on the burning zone with a peak of 360°C, and the f-CaO was acceptable but variable.

The tuning campaign proceeded in three phases. In the first phase, the swirl was reduced and the axial air increased by 10%, which lengthened the flame by roughly two meters and reduced the NOx from 700 to 560 mg/Nm3, while the f-CaO remained at target. In the second phase, the RDF injection velocity was raised by increasing the pressure of the alternative fuel channel, which kept the coarse particles suspended longer; the clinker free lime variability improved, and the RDF rate was raised to 50% thermal substitution. In the third phase, the primary air ratio was reduced from 12% to 10.5%, which improved the flame temperature and reduced the heat consumption from 3320 to 3280 kJ/kg of clinker. The final NOx, at 500 mg/Nm3, was still above the target, so the plant added an SNCR system at the preheater, which brought the NOx to 380 mg/Nm3 with an ammonia slip below 8 ppm.

The result of the campaign was a measurable improvement in all the plant’s objectives: substitution rate up from 30% to 50%, NOx down by 45% including the SNCR, heat consumption down by 40 kJ/kg, and the shell temperature peak reduced from 360 to 330°C, which extended the refractory life in the burning zone. The campaign also produced the operating matrix that the plant now uses in daily operation, and the operators were trained to use the matrix so that the optimized settings are maintained shift after shift. This case illustrates the general lesson of burner engineering: the hardware defines the possible, but only the tuning, the process integration and the operating discipline deliver the actual results.

Safety and Environmental Compliance in Firing Systems

The firing system is one of the highest-risk areas of a cement plant, and safety must be engineered into every component. The fuel storage and handling systems are designed to the applicable codes for combustible dust, including explosion relief panels, inerting systems, spark detection and suppression, and grounding against electrostatic discharge. The burner management system, which controls the ignition, the flame supervision and the shutdown sequences, is designed to a defined safety integrity level, and its logic is reviewed in a hazard and operability study before commissioning. The flame scanner must detect the flame reliably, the fuel shutoff valves must close in the required time, and the interlocks must be tested regularly. The alternative fuel feeding lines have additional hazards, including the possible presence of metal and stones, the generation of combustible gases, and the risk of fire in storage, all of which require dedicated protection.

Environmental compliance centers on the emissions that the burner and the firing system influence: NOx, CO, SO2, dust, heavy metals, dioxins and furans, and total organic carbon. The burner design and tuning reduce the NOx and the CO; the fuel selection and the kiln conditions control the SO2; and the dust is captured by the bag filter or the ESP. The firing of alternative fuels adds the risk of volatile organic emissions and the trace contaminants of the waste, which are addressed by maintaining the gas temperature in the preheater above the destruction temperature of the organic compounds and by monitoring the emissions continuously. Modern emission limits, expressed as daily averages, require a plant to keep its combustion stable and its process under tight control, which is exactly what a well-tuned burner provides. Fives Pillard supports its customers with the design documentation, the performance testing and the technical advice that allow the firing system to operate within the legal envelope under all normal operating modes.

Future Developments in Kiln Burner Technology

The development of kiln burner technology is being driven by three forces: the decarbonization of the cement industry, the rise of digitalization, and the increasing price volatility of fossil fuels. Decarbonization is pushing the industry toward the substitution of fossil fuels by biomass, waste-derived fuels and, eventually, hydrogen. The combustion of hydrogen, with its high flame speed and its different radiation characteristics, will require burners that are designed for the change in flame physics, and Fives Pillard is developing burner concepts for hydrogen co-firing and for the blending of hydrogen with natural gas. Digitalization is bringing sensors, cameras and machine learning to the burner: flame image analysis, burner tuning assistants that suggest settings from the process data, and predictive maintenance that forecasts the remaining life of the tip and the channels from the operating history. These tools will make the burner a continuously optimized instrument rather than a periodically tuned one.

The third force is the integration of the burner into the entire thermal system. The kiln burner cannot be optimized in isolation from the calciner, the preheater, the cooler and the fuel preparation, and the future burner is being developed as part of a digital twin of the kiln system, in which every process parameter is simulated and the burner settings are optimized against the simulation. The result will be kilns that are fired closer to the theoretical optimum, with less NOx, less heat loss and longer refractory life, all of which matter in an industry that must reduce its CO2 by 20–25% by 2030 to meet the Paris Agreement commitments. For the plant engineer, the implication is that the burner, which has always been a mechanical component, is becoming a data-driven instrument, and the skills that will matter in the future are the ability to read the data, to understand the process and to make decisions that balance the many conflicting objectives of kiln operation.

Training and Documentation for the Firing System

No burner installation can perform to its potential without an informed operating team, and the training of that team is as important as the hardware. The training curriculum for a Fives Pillard firing system should cover the physics of combustion, the design of the burner, the function of every component, the operating procedures, the tuning methodology and the troubleshooting guide, followed by practical sessions on the plant simulator or the actual burner during a maintenance stop. The operators should be able to interpret the flame image, to read the burner instrumentation, to make deliberate adjustments and to record them, and to recognize the early signs of the problems described in this article. The maintenance team should be able to dismantle and re-assemble the burner, to verify the geometry of the nozzles and the vanes, and to perform the dimensional inspections that protect the burner performance.

The documentation package is the second pillar of the knowledge transfer. It includes the general arrangement drawings, the nozzle and vane reference drawings, the flow curves of the air legs, the commissioning report with the reference settings, the tuning matrix, the operating manual, the maintenance manual and the spare parts list. The documentation must be kept current: every modification of the burner, every change of the reference settings and every replacement of a component must be recorded, because the documentation is the memory of the system. Many plants find that a single engineer, designated as the combustion specialist, is the most effective way to maintain the knowledge in the long term, with the training program repeated for the new engineers and the operators on a two- to three-year cycle, which matches the typical replacement cycle of the personnel in the cement industry.

Frequently Asked Questions about Fives Pillard Burners

What is the difference between a Fives Pillard Rotaflam and a conventional kiln burner?

The Rotaflam is a third-generation multichannel burner in which the primary air is divided into axial, swirl and radial channels that can be adjusted independently, giving a much wider range of flame shapes than the older two-channel designs. This flexibility is what allows the burner to handle a wide range of fuels, including petcoke and alternative fuels, without losing flame stability.

How much primary air does a modern kiln burner need?

A typical value is 8–15% of the stoichiometric combustion air, with the balance supplied as hot secondary air from the cooler. The exact value is tuned during commissioning, balancing flame stability against the reduction of the flame temperature that the primary air causes.

Why is the swirl setting important for the flame shape?

The swirl creates a central recirculation zone at the burner tip that anchors the flame and accelerates the mixing of fuel and air. Increasing the swirl shortens and widens the flame and raises the peak temperature; decreasing it lengthens and narrows the flame and spreads the heat over a longer zone.

Can a Fives Pillard burner fire alternative fuels?

Yes. The Rotaflam is available with dedicated channels for solid, liquid and gaseous alternative fuels, and installations worldwide achieve thermal substitution rates of 50–90% with the burner as the main firing point, provided that the fuel preparation and the feed systems are properly engineered.

How often should the burner be tuned?

A full tuning campaign is recommended whenever the fuel type or the production target changes significantly, and a small tuning review should be done at least once per year. Daily operation should follow the reference matrix established during commissioning, with small deliberate adjustments recorded in the burner log.

What is the service life of a burner tip?

In a typical coal-fired kiln the tip lasts 12–24 months, depending on the fuel and the operating intensity. Abrasive alternative fuels shorten the life. The tip is a replaceable component, and a spare should be kept in stock so that replacement can be done during a normal maintenance stop.

Summary and Final Recommendations

The Fives Pillard burner, and the class of modern multichannel burners that it represents, is the single most important instrument for the control of the clinkering process in a rotary kiln. This article has explained the physics of the kiln flame, the architecture of the multichannel burner, the fuel preparation that feeds it, the tuning methodology that optimizes it, the maintenance that protects it, and the safety and environmental framework in which it operates. The practical recommendations for the plant engineer are straightforward: keep the burner instrumentation calibrated, maintain the fuel preparation at the design quality, tune the burner deliberately with one parameter at a time, record every adjustment, inspect the tip and the channels at every maintenance stop, and keep the operating team trained. A plant that follows these principles will find that its burner delivers lower heat consumption, lower NOx, more stable coating, longer refractory life and the flexibility to fire the fuels that the market makes available. The burner is a capital component that is amortized over decades, but its performance is decided by the engineering discipline that surrounds it, and that discipline is what this article has set out to establish.

This file is part of the Complete Cement Technical Package (931 files) available from cementequipment.org. Respective rights holders; library copy for the licensed single user.