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Since 1942 Strommasina Corp. has been successfully producing equipment for the mining, building, oil and gas, as well as road, metallurgical industries.

Facility for lime production in a rotary furnace with a capactiy of 400 t/day

Facility for lime production in a rotary furnace with a capactiy of 400 t/day

This technical summary is intended for enterprise managers, private entrepreneurs, business owners and investors for preliminary familiarization with capacities of Samara Plant Strommashina in one of the most promising field of industrial production – metallurgical lime production.

Samara Plant Strommashina offers special equipment for lime burning, based on the latest engineering and technological developments. Samara Plant Strommashina working, which works in cooperation with its partners, has sufficient experience for design, manufacturing, supply and commissioning of lime- burning furnaces of various types and design.

In this document we review a rotary kiln with out-of-furnace heat exchangers as a calcinating unit. The proposed type of furnace is suitable for production of high-quality and reactive (А≥92%) metallurgical lime with short slacking time (mainly for steel-making and blast-furnace production) from limestone with the feed size of 20…40 (50) mm and the following parameters:

  • capacity 400 t/day;
  • fuel natural gas;
  • raw materials limestone 20…40(50) mm;
  • specific fuel consumption not more than 200 kg of fuel equivalent./t of lime;
  • mass fraction of CaO+MgO in lime at least 94%;
  • mass fraction of LOI in lime not more than 3%;
  • lime reactivity not more than 2 min;
  • dust content in treated exhaust gases not more than 20 mg/m3;
  • production resource 330 days/year.

The process flow chart of lime production in a rotary furnace with a capacity of 400 t/day is shown in Figure 1 "Flow Chart". According to this char the section includes the following basic assemblies and units:

- furnace unit with out-of-furnace heat exchangers, including:

  • lime shaft preheater;
  • dust-precipitating chamber;
  • rotary furnace;
  • shaft cooler;
  • equipment and lime cooling fans, etc.

- furnace gas cleaning system, including:

  • air cooler;
  • bag filter, etc.


ENGINEERING PROCESS DESCRIPTION

Furnace unit with out-of-furnace heat exchangers

Prepared limestone of fraction 20…40(50) mm is fed (by a conveyor, elevator, etc.) to the feed hopper (1.1) and further through charging chutes (1.22) it is supplied to the counter-flow shaft preheater (1.2). The effective capacity of the hopper is about 85 m3, which corresponds to 130 t of limestone, i.e. 4 hours of the furnace operation. The hopper (1.1) is equipped with a transmitter, which in case of raw material level lowering to a preset value sends a signal to start the limestone feed line, and when the upper limit is reached, it stops the line. To cut off the feed hopper (1.1) from the preheater (1.2), the charging chutes (1.22) are provided with finger gates (1.23).

Exhaust gases at a temperature of 850…950°С via an inlet gas duct from the dust chamber (1.4) are delivered to the preheater gas-distributing chamber (1.2). Gases enter the limestone layer in the annular heat-exchange zone, heating limestone to 700…800°С. Heat exchange takes place in countercurrent between limestone and gases. After the preheater exhaust gases are fed to gas treatment.

Partially burnt (20…30%) limestone is continuously discharged from the preheater. The discharging device (1.3) is designed as a rotating ring-type hearth. Heated limestone discharge rate is determined by the furnace capacity, and it changes gradually due to variation of the drive motor speed (rpm control). After this, heated limestone via a slanting chute is gravity fed to the charging unit (1.10) of the rotary furnace (1.11). The chute has a screening unit, where dust and fine (up to 5 mm) limestone are removed from the flow after the preheater. Spillage is supplied via a divert chute to the dust chamber (1.4) and further, via a flap valve (1.5), to a bin (1.6), from which it is removed by motor transport for disposal or consumption.

To improve resistance to high temperatures, cooling fans (1.8) for the walls of the preheater gas-distribution chamber and charging unit (1.10) elements with outlet air temperature monitoring.

Final dissociation of limestone takes place in the rotary furnace (1.11). The heat energy source for thermal processes in the furnace and the preheater is natural gas.

The optimum flare length and fuel combustion mode are adjusted (controlled) by the gas-air burner. Primary air (10…15% of that required for complete combustion of fuel) is supplied to the burner from a high-pressure fan (1.20).

Burned lime from the furnace via the hot end (1.14) is discharged to the shaft cooler (1.16), where it is cooled down to 50…80°С.

Cooling air is supplied from the fan (1.17) into the air-distribution chamber in the centre of the cooler. Passing through the lime layer, it is heated up to 300…350°С due to the physical heat of lime. Heater air via a separate gas duct is supplied to the furnace hot end (1.14) and is used for fuel combustion. Air flow rate through the lime cooler enables fuel combustion with the excess coefficient α of 1.1…1.15.

For lime discharge from the cooler (1.6) one vibration feeder (1.19) is used, feeding lime to a belt conveyor (1.21).

To exclude the ingress of dust-laden air from the cooler discharge chute and above the vibration feeder pan, air tapping to the dust-removal system will be provided.

Furnace gas treatment

Exhaust gases after the preheater are supplied via the discharge gas duct to gas treatment. To reduce the gas temperature to an acceptable level for operation of the gas-cleaning equipment a recuperation cooler (2.1) will be installed and air inflow will be arranged (via an adjustable valve 1.3). Dust residual content in exhaust gases after gas treatment will not exceed 20 mg/m3 due to application of a bag filter (1.4).

The gas recuperating cooler (2.1) is provided with a lock feeder (2.2) to discharge collected dust (0.2…1.0 mm) to a container or a dump truck. Dust from the bag filter (2.4) will be supplied by an auger conveyor (2.7) to the elevator (2.8) to deliver it to a silo (2.9). The dust silo (2.9) is equipped with a blade gate (2.10). To load dust to a cement truck a discharge hose (2.11) is used.

Movement of combustion products around gas ducts and maintenance of required pressure in the furnace hot end (1.14) is ensured by a smoke exhauster (2.5). Dust-free exhaust gases are discharged to the atmosphere via a smoke stack (2.6).

 

BASIC RESOURCES REQUIRED

Raw carbonated feedstock

Demand of the furnace for prepared limestone of 20…40(50) mm with the furnace capacity of 400 t/day of lime of required quality is about 760 t/day. Taking into account the screening rate, the limestone amount will be about 800 t/day. Raw material demand data are provided in Table 1.

Table 1. Limestone demand


Limestone consumption rate

t/h

t/day

thousand t/year

Limestone specific consumption, t/t of lime

For burning
(after check screening)

31.6

760

250.8

1.9

For the furnace
(before check screening)

33.3

800

264.0

2.0

* Production resource: 330 days/year

Fuel

Natural gas will be used as fuel. Its calorific capacity is 8,000 kcal/m3 (mean value). Fuel is supplied to the furnace via a special burner.
Natural gas consumption of the rotary furnace is about 3,060 m3/h. The required amount of fuel is supplied to the furnace via a gas pipeline at 0.25…0.3 MPa. Natural gas demand data are provided in Table 2.

Table 2. Natural gas demand of the furnace


Item

m3/h

m3/day

thousand m3/year*

Gas specific consumption
m3/t of lime

Rotary furnace

2,850

69,768

23,023,440

173
(200 kg of fuel equivalent./t)

* Production resource is 330 days/year without regard to furnace preheating, startup and shutdown.

Compressed air

Compressed air is used to operate the regeneration system of the gas cleaning filter, instrumentation and the furnace charging unit.

To ensure reliable operation of filter regeneration systems and other users, dehydrated air (per class 1 of GOST 17433-80) should be supplied at 0.55…0.6 MPa and flow rate of 540 m3/h. Compressed air must not contain any condensed moisture or water mist: dew point (-)40°С, oil concentration – up to 0.05 mg/m3, solid particle size – up to 5 μm.
Compressed air demand data are provided in Table 3.

Table 3. Compressed air demand data


Item

m3/h

m3/day

thousand m3/year*

Furnace gas cleaning filters

240

5,760

1,900.8

Control equipment

180

4,320

1,425.6

Furnace charging unit

120

2,880

950.4

Total per section

540

12,960

4,276.8

* Production resource: 330 days/year

Power supply

The main power consumers are process draft equipment, the furnace drive, the process control system, etc.
The installed power of equipment at 380/220 V (50 Hz) with breakdown by assembles is shown in Table 4.

Table 4. Installed power of equipment


No.

Section

Power, kW

1

Furnace installation with heat exchangers

430

2

Furnace gas treatment

450

Total installed power

880

*Note: Rated power of installed equipment is tentative and will be refined at the engineering design stage (basic engineering) after final determination of the equipment type and manufacturer.

The total installed power of the section excludes power consumption for electric lighting (indoor, outdoor), lifting equipment, household needs, ventilation and conditioning systems, fire-extinguishing systems and other auxiliary equipment.
Installed power of process power consumers is about 880 kW. Consumed power is tentatively estimated as 60% of installed power, i.e. 528 kW or about 31.6 kW/t of lime.

ENGINEERING SUPPORT

Engineering

Engineering development is performed by Samara Plant Strommashina (mandatory supply by Plant Strommashina), considering the terrain relief, locations of utilities, buildings, transportation routes, foundations, steel structures at the construction site, as well as feedstock properties, fuel characteristics and requirements to the final product. Engineering development is carried out for the lime production site with issuance of assignments for development of design and estimate documentation.
Engineering development includes the following stages:

- basic data (study and processing of background data, technical assignment development, agreement and approval);
- basic engineering (design – stage П, including basic automation;
- detailed engineering (design – stage Р, including detailed automatic process control system).

PROJECT MILESTONES

Project implementation schedule

Construction of a facility for lime production in a rotary furnace Ø3.6x60 m with out-of-furnace heat exchangers and auxiliary equipment can be completed approximately in 19 months after signing a contract.

The schedule will be finalized by the Customer, considering resource planning and capacities of installation contractors.
The below calendar schedule is based on experience of Plant Strommashina and starts from the contract date.

  • Basic data (Strommashina) – within 2–4 months
  • Basic engineering (Strommashina) – within 8–9 months;
  • Detailed engineering (Strommashina) – within 10–11 months;
  • Equipment and materials supply (including PCS and electric drives) – within 12–14 months;
  • Construction and installation works, commissioning works, cold tests – within 18 months;
  • Start-up, furnace assimilation and guarantee tests – within 19 months.

As agreed upon, Strommashina can act as a key-turn contractor.
The budgeted cost of all project expenses will be provided only after basic data study and approval.
Consolidated (specified) project costs will be determined only upon completion of design works.

SUMMARY

Advantages of Strommashina's proposal:

  • Work with a single contract – original equipment supplier, provider of design works and services, installation, commissioning and post-warranty service;
  • Possible provision of financial guarantees – securing your advance payment by a bank guarantee;
  • Availability of a sufficient number of references for supplies of rotary units (ball mills, drying drums, burning furnaces, drum-type coolers, etc.) – more than 1,000 pieces of equipment supplied during the plant's operation;
  • Uniform and stable quality of the final product due to application of rotary furnaces, and considerable specific fuel cost reduction per tonne of product, if a recuperation system is used;
  • Possibility to use a non-waste production technology by the Customer's request: undersize and dust processing into an additional product – mineral powder or micro-marble (microcalcite);
  • Experience in application of the latest automatic process control systems based on Modbus, Profibus and other protocols;
  • Uninterrupted and scheduled supply of original spare parts and post-warranty services to reduce the Customer's operating costs and to increase industrial safety.