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Maerz® Lime Burning Technology

Our Company 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 Flow Regenerative (PFR) Lime Kiln«, characterised by its high thermal efficiency and superior lime 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 a patented system to apply pulverised solid fuels was introduced. Today Maerz offers designs for PFR Kilns with nominal capacities between 100 and 800 tpd and with firing systems for virtually all types of liquid, gaseous and pulverised solid fuels. As a further milestone, in the late eighties, Maerz introduced the »Maerz® Finelime Kiln«. This vertical-shaft kiln type allows the calcination 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,

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Our Achievements 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 customers. 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, such as production capacity, type of fuel, raw material feed size, lime quality required, etc. the decision for a certain kiln type is made by evaluating the balance between cost, technological reliability and flexibility.

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

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

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

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 comprehensive scope of lime burning equipment.

In 2006 Maerz joined the Polysius Group, becoming the centre of lime business activities of the entire Group. With Polysius know-how and personnel resources, 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.

Supported by a global network of representatives and partners, Maerz can present the largest 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.

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

Lime is one of the most widespread and versatile chemicals produced and applied worldwide. Quicklime and hydrated lime have been used in many civilisations 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, whereof 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

The most important consumers of lime, dolomitic lime and dolomite are: 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 - s andlime bricks, aerated concrete bricks Chemical industry -m  anufacture 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 - s tabilisation of road beds for high performance roads - c onstruction of airport runways, parking lots and railway tracks PCC industry - paper industry - paints and coatings - plastics

Types of Kilns and Calciners Kiln type

Rectangular PFR Kiln

Circular PFR Kiln

Finelime Kiln

E1 – E6

R1 – R5

F1 – F3

Capacity

[tpd]

100 – 400

300 – 800

200 – 400

Stone size

[mm]

30 – 120

30 – 160

15 – 40

Heat input

[kJ/ kg] [kcal/kg]

3390 – 3650 810 – 870

3390 – 3650 810 – 870

3310 – 3560 790 – 850

high reactivity lime

high reactivity lime

high reactivity lime

Key criteria

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

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

Product Portfolio Annular Shaft Kiln

Single Shaft Kiln

Preheater Rotary Kiln

Suspension Calciner

A1 – A3

H1 – H5

200 – 600

50 – 300

500 – 1200

300 – 1200

15 – 200

10 – 100

10 – 50

0.03 – 2

3800 – 4100 910 – 980

4100 – 4610 980 – 1100

4820 – 5650 1150 – 1350

5450 – 5860 1300 – 1400

high CO2-content in off-gas

medium to hard burnt lime

high production rate low sulphur product

finest raw material size

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

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 parallel 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 simultaneously 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

Circular PFR Kiln

Finelime 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 geometry this kiln type is simple to manufacture with reduced requirements for steel structure and refractory materials.

For larger capacities, e.g. from 300 to 800 tons per day, kilns of circular cross section are recommended. 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 radially around the complete shaft perimeter, thereby guaranteeing an even heat distribution.

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«.

This straightforward and costefficient kiln type is mainly applied 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 gaseous, liquid and pulverised solid fuels.

Since 1966, more than 200 circular Maerz® Kilns operating with gaseous, liquid and pulverised solid fuels, or a combination of these, have been built worldwide.

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

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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 regenerative preheating of combustion air, the Finelime Kiln is able to burn limestone sized between approx. 15 and 40 mm at thermal efficiencies superior to conventional PFR Kilns. Since 1989 – the year of its introduction – Maerz has built approx. 35 Finelime Kilns worldwide.

1 Fig. 1 Pusher of the Preheater. Fig. 2 View into a Rotary Kiln. Fig. 3 Preheater Rotary Kiln.

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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 partially calcine the limestone. The modular preheater design most effectively combines heat transfer with optimal accessibility for maintenance during operation. 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 knowledge of lime burning such as gas flow patterns in bulky material beds.

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Rotary Kilns Sulphur Bypass System Today‘s steel industry has a growing demand for lime with minimal sulphur content. 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 input 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 screening and classifying process. The sulphur bypass system provides a very effective solution to produce low sulphur quicklime even when using highly contaminated fuels.

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Large photo New-Generation Lime Shaft Preheater. Fig. 4 The Sulphur Bypass System.

Suspension Calciner The POLCAL® process was developed by Polysius based on their extensive experience 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 suspension 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 residence time in a conditioning drum installed downstream the reaction chamber, the degree of reactivity of the burnt material can readily be adjusted to meet customer requirements.

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Shaft Kilns – Suspension Calciners

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Annular Shaft Kiln

Single Shaft Kiln

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

Special applications of lime, e.g. in the production of sandlime bricks and aerated concrete bricks or blocks, require hard burnt, low reactivity quicklime. The RCE designed single shaft lime kiln satisfies this requirement.

The main feature of this kiln type is the continuous stream of exhaust gases with a high CO2-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 characteristics have made the Annular Shaft Kiln the preferred choice for PCC and soda production. A wide range of fuels can be applied on this kiln with production ranging between 200 and 600 tons per day.

Based on the design of the “RCE High Temperature Kiln”, mainly used in the refractory materials industry for sintering magnesite, dolomite and alumina, and in response to market requirements, a high efficiency single 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.

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.

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, commissioning 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 industry have been built since 1950 in some 60 countries 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 CO2-content and the production of low sulphur lime, rotary kilns, single shaft kilns, annular shaft kilns and suspension calciners complement Maerz’s product portfolio.