Maerz®

Lime Burning Technology

Our Company

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Maerz Ofenbau AG was established in 1950 in Zurich, Switzerland, by Austrian magnesite producers to design and sell open hearth furnace technology to the worldwide steel industry.

In 1965 Maerz began the design and construction of the »MAERZ® Parallel FlowRegenerative (PFR) Lime Kiln«, characterisedby its high thermal efficiency and superiorlime quality, now generally known as the »MAERZ® PFR Kiln«.

The initial design was an oil-fired lime kiln of 150 tpd capacity. Soon larger units were designed and gas firing technology was added to oil firing. In the late seventies apatented system to apply pulverised solidfuels was introduced. Today Maerz offersdesigns for PFR Kilns with nominal capacitiesbetween 100 and 800 tpd and with firing sys-tems for virtually all types of liquid, gaseousand pulverised solid fuels.

As a further milestone, in the late eighties,Maerz introduced the »Maerz® Finelime Kiln«.This vertical-shaft kiln type allows the calci-nation of small-size limestone and dolomite, which in the past had to be processed in rotary kilns with significantly lower thermal efficiency, i.e. higher heat consumption.

In 1995 RCE Industrieofenbau Engineering GmbH, located in Radenthein, Austria, a specialist in the field of furnaces and kilns for the production of refractory materials,

Our Achievements

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became a subsidiary company of Maerz, adding its high-efficiency single shaft kiln to the existing product portfolio.

To satisfy the steadily increasing market demand in Eastern Europe, Maerz establisheda subsidiary engineering division – Maerz Ofenbau s.r.l. – in Timişoara, Romania, in 2005.

In 2006 Maerz joined the Polysius Group, becoming the centre of lime business activi-ties of the entire Group.

With Polysius know-how and personnel re-sources, Maerz now also offers rotary kilns, annular shaft kilns, suspension calciners and equipment up- and downstream of the lime kilns, thus turning into a full-line supplier of kilns and associated equipment for the lime industry.

By combining Maerz, Polysius and RCE’s know-how and experience in the lime burning technology field, Maerz is in a unique position to offer tailor-made solutions to its cus-tomers.

The different kiln systems – such as PFR Kilns, Single Shaft Kilns, Rotary Kilns or Suspension Calciners – do not compete with, but complement each other.

Depending on the application conditions, suchas production capacity, type of fuel, raw mat-erial feed size, lime quality required, etc. the decision for a certain kiln type is made by evaluating the balance between cost, techno-logical reliability and flexibility.

It is Maerz’s policy – on the basis of an extensive product portfolio – to carefully assess all initial conditions before recommending the most suit-able kiln technology to its customers to meet the specific project conditions and to achieve the required product quality.

Maerz – the world leader in the construction of lime kilns – is not only in a position to offer the most energy-efficient type of lime shaft kiln existing to date but also the most comprehen-sive scope of lime burning equipment.

Supported by a global network of representa-tives and partners, Maerz can present the lar-gest number of reference plants installed worldwide in the lime industry by one single company.

Large photo + Fig. 1 Headquarters of Maerz Ofenbau AG in Zurich, Switzerland.

Fig. 2 – 4 From the Idea to the Start of Production.

Lime is one of the most widespread and ver-satile chemicals produced and applied world-wide.

Quicklime and hydrated lime have been used in many civilisa-tions for more than 3000 years. Starting from the construction and building industry in the early days, the uses of lime, dolomitic lime and dolomite have become almost countless.

Vital in the steel, building and chemical industries, as well as in agriculture, lime is a basic raw material that has made an essential contribution to many of the achievements of our modern world.

Global production of lime is estimated to be approx. 300 million tons per year, where-of the sales-relevant portion amounts to approx. 120 million tons per year. In industrialised countries the yearly per capita consumption of lime products amounts to approx. 80 kg.

Applications of Lime

Iron and steelmaking- capturing of impurities in

the steel bath- iron ore sintering- desulphurisation

Non-ferrous metals- beneficiation of non-ferrous

metal ores, e.g. copper- recovery of gold and silver

in cyanide extraction- flotation processes for lead,

nickel, zinc, molybdenum and uranium

Construction and building- mortars and plasters- sandlime bricks, aerated

concrete bricks

Chemical industry- manufacture of sodium

alkalis, e.g. soda ash- production of calcium carbide

Environmental applications- treatment of water, waste

water and sewage- air pollution control

Agriculture- liming of soils, forests and

lakes- compound fertilisers

Soil stabilisation- stabilisation of road beds

for high performance roads- construction of airport

runways, parking lots and railway tracks

PCC industry- paper industry- paints and coatings- plastics

The most important consumers of lime, dolomitic lime and dolomite are:

Types ofKilns and Calciners

Kiln type

Capacity [tpd]

Stone size [mm]

Heat input [kJ/kg] [kcal /kg]

Key criteria

Services

• Revamping• Upgrading• Modernisation• Alternative Fuels• Automation• Spare parts

RectangularPFR Kiln

E1 – E6

100 – 400

30 – 120

3390 – 3650810 – 870

high reactivitylime

PFR Kilns

• Multi-fuel firing systems• Conversion to alternative fuels• Advanced charging technology for increase of quarry yield and production

CircularPFR Kiln

R1 – R5

300 – 800

30 – 160

3390 – 3650810 – 870

high reactivitylime

FinelimeKiln

F1 – F3

200 – 400

15 – 40

3310 – 3560790 – 850

high reactivitylime

Product Portfolio

Annular ShaftKiln

A1 – A3

200 – 600

15 – 200

3800 – 4100910 – 980

high CO2-content

in off-gas

Annular Shaft Kilns

• Application of solid fuels

Single Shaft Kilns

• Conversion of mixed feed kilns to solid fuel dust firing with significant increase of kiln capacity

Rotary Kilns

• Conversion to preheater kilns • Sulphur bypass system

Single ShaftKiln

H1 – H5

50 – 300

10 – 100

4100 – 4610 980 – 1100

medium to hardburnt lime

PreheaterRotary Kiln

500 – 1200

10 – 50

4820 – 56501150 – 1350

high production ratelow sulphur product

SuspensionCalciner

300 – 1200

0.03 – 2

5450 – 58601300 – 1400

finest raw materialsize

PFR Kilns

The PFR (Parallel Flow Regenerative) kiln type is characterised by two vertical shafts connected by a cross-over channel.

This allows parallel flow heating, i.e. the paral-lel flow of limestone and hot gases as well as regenerative preheating of the combustion air in one shaft (the burning shaft) whilst the mixture of combustion gases and lime cooling air simultane-ously preheats the limestone in the second shaft (the non-burning shaft). Each shaft cycles through the burning and non-burning mode at intervals of approx. 10 to 15 minutes.

The Parallel Flow Principle is ideal for producing high reactivity quicklime at the highest thermal efficiency of all modern lime kilns.

PFR Kilns are available for capacities from 100 to 800 mt/day and can be fired with gaseous, liquid and pulverised solid fuels.

Depending on the required production capacity, the limestone grain size to be processed and the fuels available, PFR Kilns of rectangular, circular or Finelime design are proposed.

Parallel Flow Regenerative Shaft Kilns

Rectangular PFR Kiln

The simplest design of a PFR Kiln is to place two shafts with rectangular cross section side by side lengthwise in such a manner that the kiln gases can flow directly from one shaft to the other via a direct cross-over channel. Because of its geom-etry this kiln type is simple to manufacture with reduced re-quirements for steel structure and refractory materials.

This straightforward and cost- efficient kiln type is mainly ap-plied for output rates up to 400 tons of burnt lime or dolomite per day.

As from 1966, Maerz has built roughly 200 rectangular kilns worldwide operating with gas-eous, liquid and pulverised solid fuels.

Circular PFR Kiln

For larger capacities, e.g. from 300 to 800 tons per day, kilns of circular cross section are rec-ommended. These kilns feature circular ring channels collecting the combustion gases before they enter the non-burning shaft via the cross-over channel. The gases exit the burning shaft and enter the non-burning shaft ra-dially around the complete shaft perimeter, thereby guaranteeing an even heat distribution.

A bucket positioned vertically above each shaft is used for charging raw stone into the kiln shafts. Stone distribution is further improved by rotat-ing the bucket during charging from conveyor belts or vibrat-ing feeders. The circular shaft design facilitates uniform stone and fuel distribution during charging, as well as calcination throughout the complete shaft cross section.

Since 1966, more than 200 cir-cular Maerz® Kilns operating with gaseous, liquid and pulver-ised solid fuels, or a combination of these, have been built world-wide.

Finelime Kiln

Typical stone sizes processed in conventional vertical shaft kilns are larger than 30 mm. Stone sizes of 6 to 30 mm can be calcined in rotary kilns, but with lower thermal efficiency. To solve this shortcoming, Maerz has developed a special type of PFR Kiln – the »Finelime Kiln«.

While maintaining the unique features of PFR Kiln principles, i.e. the parallel flow of material and combustion gases in the burning zone and the regenera-tive preheating of combustion air, the Finelime Kiln is able to burn limestone sized between approx. 15 and 40 mm at ther-mal efficiencies superior to con-ventional PFR Kilns.

Since 1989 – the year of its introduction – Maerz has built approx. 35 Finelime Kilns world-wide.

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Large photo Rectangular PFR Kiln.

Fig. 1 Circular PFR Kiln.

Fig. 2 Finelime Kiln.

Fig. 3 Startup burner.

Fig. 4 Refractory lining work.

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Fig. 1 Pusher of the Preheater.

Fig. 2 View into a Rotary Kiln.

Fig. 3 Preheater Rotary Kiln.

Preheater Rotary Kiln

Preheater Rotary Kilns are the preferred technology for the burning of limestone and dolomite if the following conditions apply:

• high production capacity, preferably greater than 1,000 tpd

• small stone feed size, e.g. 15 to 40 mm

• maximum fuel flexibility

• production of low sulphur lime (e.g. for the steel industry) despite the usage of cheap, high sulphur fuels.

The energetic efficiency of a rotary kiln is highly enhanced by a shaft preheater that uses the kiln off-gases to preheat and par-tially calcine the limestone.

The modular preheater design most effec-tively combines heat transfer with optimal accessibility for maintenance during opera-tion.

Our technology of preheater rotary kilns is based on the joint know-how of Polysius and Maerz.

Polysius contributes its broad knowledge of rotary kilns and its R&D capabilities while Maerz contributes profound process knowl-edge of lime burning such as gas flow pat-terns in bulky material beds.

Rotary Kilns

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Large photo New-Generation Lime Shaft Preheater.

Fig. 4 The Sulphur Bypass System.

Sulphur Bypass System

Today‘s steel industry has a growing de-mand for lime with minimal sulphur con-tent.

Furthermore, the sharp increase in fuel costs has created the necessity of looking for cheaper fuel sources in order to limit operating costs. Unfortunately, the usage of cheaper fuels often means an increased in-put of sulphur and other impurities into the kiln system.

A special “sulphur bypass system” was developed by Polysius to allow the firing of high sulphur fuels for the production of low sulphur lime in rotary kilns being equipped with a shaft preheater.

In this novel system, the countercurrent streams of material and kiln exhaust gases are separated between preheater and rotary kiln. The material is subject to a hot screen-ing and classifying process.

The sulphur bypass system provides a very effective solution to produce low sulphur quicklime even when using highly contami-nated fuels.

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Suspension Calciner

The POLCAL® process was developed by Polysius based on their extensive experi-ence in the field of thermal treatment of bulk materials acquired over many decades. It is especially suitable for treating fine-grained limestone and dolomite.

Materials within a grain size range of 0.03 to 2 mm can be processed in this gas suspen-sion process.

POLCAL® systems have several vertically arranged cyclone stages and a reactor for thermal treatment of the raw materials as well as one or several cooling cyclones to cool the treated product. The individual cyclone stages are interconnected by gas ducts.

With production capacities ranging between 300 and 1,200 tpd of burnt product, liquid, gaseous and – to a certain extent – solid fuels are applicable. The fuel is supplied via several injectors arranged around the reactor.

By varying the temperature and/or resi-dence time in a conditioning drum installed downstream the reaction chamber, the de-gree of reactivity of the burnt material can readily be adjusted to meet customer re-quirements.

Shaft Kilns – Suspension Calciners

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Large photo Single Shaft Kiln.

Fig. 1 Suspension Calciner.

Fig. 2 Cyclone of the Suspension Calciner.

Fig. 3 Detail of an Annular Shaft Kiln.

Fig. 4 Annular Shaft Kiln.

Fig. 5 Oil Burner of an Annular Shaft Kiln.

Annular Shaft Kiln

The Annular Shaft Kiln is characterised by its annular shaped shaft cross section lo-cated between an outer and inner refractory lined cylindrical steel shell.

The main feature of this kiln type is the continuous stream of exhaust gases with a high CO

2-content, ranging between 26 and

32 %, depending on the type of fuel used.

Furthermore, the kiln allows the adjustment of the reactivity of the quicklime produced from soft to medium burnt. These charac-teristics have made the Annular Shaft Kiln the preferred choice for PCC and soda pro-duction.

A wide range of fuels can be applied on this kiln with production ranging between 200 and 600 tons per day.

Single Shaft Kiln

Special applications of lime, e.g. in the pro-duction of sandlime bricks and aerated con-crete bricks or blocks, require hard burnt, low reactivity quicklime. The RCE designed single shaft lime kiln satisfies this require-ment.

Based on the design of the “RCE High Tem-perature Kiln”, mainly used in the refractory materials industry for sintering magnesite, dolomite and alumina, and in response to market requirements, a high efficiency sin-gle shaft kiln for the calcination of limestone, dolomite and magnesite was subsequently designed and patented. The main features of this novel single shaft kiln type are:

• the use of cooled, retractable side burners

• a wide range of product reactivity due to the easy adjustability of operating temperatures and

• the high specific output per shaft cross section.

Services

Research and Development

Excellent technological competence is the key to winning over and retaining customers as well as to exploiting growth potential in existing and new markets. Increasing the size of production units and improving the operating economy of production plants are main development priorities.

Maerz makes use of the Polysius Research Centre. With its modern equipment, this is one of the leading institutions for technological development in the mineral industry.

Customer Services

Maerz can assist their customers in many different ways and offers the following services:• Project feasibility studies• Engineering services• Supply of key equipment for lime, dolomite

and magnesite kiln plants• Turn-key erection of complete kiln plants• Supervision services for erection, commis-

sioning and operation of kiln plants• Spare parts supply• Technical audits on kiln plants in operation• Training of operating and maintenance

personnel• After sales services including consulting for

operating and maintenance problems• Elaboration of modernisation proposals.

The World Leader in Lime Kilns

References

About 500 new kilns for the lime and dolomite in-dustry have been built since 1950 in some 60 coun-tries by Maerz, Polysius and RCE.

Since their introduction in the late 1950’s, the Maerz PFR Kilns have become standard equipment in the lime and dolomite industry. Their superior thermal efficiency, paired with the flexibility of being able to apply virtually all types of fuel and raw materials, has made them an excellent choice whenever the installation of new calcining equipment is an issue.

For special applications, such as production capacities of more than 1000 tons per day, the requirement to burn powdery raw material or to produce low reactivity lime, a continuous off-gas flow from the kiln with high CO

2-content and the production of

low sulphur lime, rotary kilns, single shaft kilns, annular shaft kilns and suspension calciners complement Maerz’s product portfolio.