bypass systems

System Information

Bypass Systems

Lafarge - Lyon

Offer no: LAFF-08-01-bp-s Rev.00

France - England

A TECAdvanced Process Technology

Kasernstrasse 16-18 35 000 KremsA U S T R I A

Tel: + 43-273-275-680 Fax: + 43-273-275-680-15 [email protected]

www.atec-ltd.com

Krems,18.08.2008

Rev.0 / 14.08.2008 page 2 of 17 LAFF-08-01-bp-s System Information 080818.doc

CONTENT

1. BASIS DATA FROM LAFARGE........................................................................... 32. PROCESS DESIGN ALTERNATIVES.................................................................. 3

2.1 ENVIRONMENTAL CONDITIONS .......................................................................... 32.2 SPECIFIC GAS VOLUME.................................................................................... 42.3 BYPASS RATE ................................................................................................. 42.4 BYPASS DUST LOAD ........................................................................................ 6

3. EQUIPMENT DESIGN .......................................................................................... 73.1 GENERAL BYPASS SYSTEM DESIGN .................................................................. 73.2 TAKE OFF CHAMBER......................................................................................... 93.3 QUENCH CHAMBER........................................................................................ 103.4 FILTER AND SILO ARRANGEMENT .................................................................... 113.5 BYPASS DUST TRANSPORT............................................................................. 123.6 FAN EQUIPMENT............................................................................................ 133.7 DESIGN OVERVIEW BASED ON LAFARGE DATA................................................. 14

4. PROJECT PROCEDURE AND TENDERING..................................................... 155. PROJECT PLANNING........................................................................................ 166. ENCLOSURES ................................................................................................... 17


1. BASIS DATA FROM LAFARGE

Lafarge has the intention to install a total of seven chloride bypass systems in various plants in France and England.

The basis data provided by Lafarge are

Clinker production 1000 t/d 2500 t/d 5000 t/dBypass gas take-off 4000 Nm³/h 5000 Nm³/h 6000 Nm³/hNo. of plants 4 2 1

Lafarge requested ATEC to provided system information as well as costing and planning data for the above specified bypass application.

2. PROCESS DESIGN ALTERNATIVES

As the basic data provided by Lafarge would allow numerous design alternatives certain design data have been assumed by ATEC to limit the number of possible bypass systems.The assumptions made and the implications of various technical data are described below.

2.1 Environmental Conditions

The process design was based on the following environmental conditions for all alternatives calculated;

Ambient air temperature: 30 °CHumidity: 40 %Plant Level: 200 m

The ambient air temperature has a major effect on the cooling air quantity and has been assumed on the high side.

The actual plant level does not affect the process design as such but is important for the design specification of fan and filter system.


2.2 Specific Gas Volume

The specific gas volume is dependant on a. the fuel utilised in the main burnerb. if the kiln is equipped with a preheater or Precalcinerc. the fuel split between main burner and calciner burner

Preheater Kiln:For a preheater kiln the specific gas volume is typically between 1,0 Nm³/h (for coal firing) to 1,2 Nm³/h for gas firing. Alternative fuel combustion ( RDF or plastic) creates similar quantity of combustion gas as with natural gas combustion. However depending on the chemical composition of the alternative fuel used and its moisture content there can be a large fluctuation in the specific gas volume extracted at the bypass position.

Precalciner Kiln:For a precalciner kiln the specific gas volume is typically between 0,5 Nm³/h (for coal firing) to 0,6 Nm³/h for gas firing with a 50% to 50%split between main burner and calciner burner.The influence of alternative fuel as described for the preheater kiln is also applicable for the Precalciner kiln.

2.3 Bypass Rate

The required bypass rate is determined by considering the volatility of various chemical compounds. The graph below shows the potential reduction of the various chemical compounds in relation to the bypass rate.


Based on the result of the process design calculation completed in our technical centre a guarantee curve is provided by ATEC identifying the guaranteed max. hot meal chloride content at a fixed bypass rate and varying chloride input as may occur in real operating condition.

For indication of the expected operation condition with and without bypass the industry standard VDZ curves as shown below are used by ATEC.

0,0

0,5

1,0

1,5

2,0

2,5

0,04 0,05 0,06 0,07 0,08 0,09 0,10

Cl-c

onte

nt[%

,loi

-free

]

Cl-input (raw material + fuel) based on clinker [%]

Typical Comparison of hotmeal chlorine content (at 5 % bypass-ratio)

expected without bypass

guaranted with bypass

calculated with bypass


As Lafarge has specified and calculated the required bypass gas quantity for the given clinker production the ATEC guarantee curve is not applicable in this case.

Based on the Lafarge data for clinker production and bypass gas quantity taken from the kiln inlet on one side and the ATEC assumed specific gas volume on the other side the bypass rate is calculated.

The data as shown in the table below have to be confirmed by Lafarge.

2.4 Bypass Dust Load

Depending of the actual plant design the bypass dust load can vary widely and has a direct effect on the cooling air required and subsequently on the equipment and duct sizing.

Typical values for bypass dust loads are as follows;

Preheater kiln: 250 g/Nm³ normal400 g/Nm³ for dusty kiln inlet areas

Precalciner kiln: 400 g/Nm³ normal600 g/Nm³ for dusty kiln inlet areas800 g/Nm³ in exceptional cases

General FLS, KHD and ATEC kiln tend to have a cleaner kiln inlet atmosphere due to the meal inlet from the kiln inlet back wall compared to the Polysius kiln design with the meal inlet from the side of the kiln inlet chamber.However this will have to be investigated on a case by case basis.

The reason for the increased dust load of the precalciner kiln compared to the preheater kiln is the reduced kiln gas quantity for the same bypass rate and the lower specific density of precalcined dust.


3. EQUIPMENT DESIGN

There are specific ATEC proprietary equipment utilised in the ATEC bypass system e.g. the quench chamber without lining and resulting low maintenance requirements.

On other equipment design the actual preheater geometries and available ground space have a direct bearing on design and cost.

The main equipment sections are described below

3.1 General Bypass System Design

Due to the very efficient quenching of kiln gas with ambient air there is the possibility to have a single stage quenching in less then 1,4 m height space for the quenching chamber. This is the standard for a bypass system design.

Alternative it may be required to install 2 steps of quenching to allow a reduction of bypass dust generated by appr. 50%. This is accomplished by installation of a cyclone after the first stage quenching. The oversized particles (appr. 20 microns) will be returned to the kiln inlet chamber and the remaining dust transported to the second quenching and subsequent filtration plant.The internal chloride circuit created by returning dust to the kiln inlet is very low as the larger particles have a low specific surface for chloride to adhere to in comparison to the fine dust passed on further. Additionally there is the possibility to feed the oversized particles to the cyclone riser to act as seed particles for SO2 or chloride scrubbing if need be.

Such a system is successfully in operation since January 2005 at Castle Cement in England and has been proven very successfully for the reduction of bypass dust quantity and in terms of reliability.

Another reason may be the feed of hydrated lime for reduction of SO2 or chloride. By allowing the feed point to be in a higher temperature zone between the twoquenching systems the chemical reaction and therefore the reduction of SO2 or chloride will be done more efficiently.


Please see typical flow diagrams of a standard bypass system as well as the 2-stagequenching system with dust separation via a cyclone.

Standard single stage quenching with dosing system

2- stage quenching with cyclone


Pictures from bypass installation at Castle Cement

3.2 Take off chamber

There is no fixed design for the take off chamber as the design has to be adapted to the geometry of the preheater and the position of the take off point.

Generally the position of the take off point is at the kiln riser above the kiln. However specific situation may require to move the position to the side of the kiln riser.

For design of the take off chamber ATEC has the following guide rules;

a. Preferred gas velocity at the take off point is less 10,0 m/s to keep the amount of bypass dust especially coarse dust particles to a minimum i.e. size of take off point is designed accordingly

b. As short as possible to avoid possible areas of sticking. This depends largely on the lowest possible position of the quench chamber

c. Inclination of take of chamber bottom plate to be preferably larger than 50° from the horizontal.

The length of the take off chamber may vary between 3,0 m to 6,0 m based on previous installation.


Typical Take off chamber design

3.3 Quench Chamber

The ATEC quench chamber is unique in its design, operation flexibility and mixing efficiency.

The design does not require that any section of the quench chamber to be lined with refractory material although the kiln gas is entering in the bottom opening with a temperature of appr. 1100°C and leaved the quench chamber at 200°C after a quenching section of less than 1,4 m in length.


The quench chamber consists of a outer section for the ambient air and an inner tube for the kiln gas. The ambient air is forced via the cooling air fan through slots in the inner tube and thereby accelerated up to 40 m/s. This creates an intensive mixing zone within the inner tube.

This design is possible due to the special material developed (temperature difference of over 900°C over a distance of 1,4 m) in co-operation with the steel industry

For the quenching efficiency plant measurements at Castle Cement have proven that the temperature difference measured over the cross section of the mixed gas duct in a distance of 5 meters after the 1-stage quenching was less than 50°C and after the second stage quenching was less than 20°C.

The quenching efficiency is dependant on the gas turbulence (velocity) in the mixing chamber. As the bypass system will not always be operated at maximum design capacity the subsequent gas volumes will be lower. To compensate for lower gas velocities the ATEC quench chamber is divided in 2 or three sections on top of each other as required. When the system is operated at a reduced bypass rate the fresh air inlet gate will close the cooling gas inlet to the upper section of the quench chamber and such allows reduced gas flow to the lower section with a lower cross sectional area and thereby maintaining the required gas velocity.

However keep in mind that a minimum fluctuation of the bypass rate is the basis for a trouble free bypass operation over a long period.

3.4 Filter and Silo Arrangement

To avoid operational problems due to sticking the filtration plant shall be located as close as possible to the preheater.We have made very good experience with bag filters whereby due to the nature of the gas and the temperature filter bags with Teflon membrane and glass fibre base material is used.

Although no refractory lining is required except for the take off chamber there is the need for insulation of the complete system from quench chamber to the filter plant including filter to ensure that the gas temperature during normal operation as well as emergency shutdown condition above the acid dew point.

The design of the mixed gas ducting from the quench chamber to the filter plant shall allow for step pipe routing avoiding any sticking material. The recommended inclination is 60° or more from the horizontal. Resulting thereof are longer duct works the further the filter plant is positioned from the preheater.


In all the bypass installation completed so far there were never unexpected problems in the actual operation of the bypass system itself but only in the dust handling.

Therefore were reasonable possible ATEC is positioning the filtration plant at the top of the bypass dust silo. This way no material handling equipment is required between the dust storage and the filter. Further the silo acts like a large drop out box and only the front bags of the filter are fully loaded with bypass dust and extend the expected life of the filter bags. Although no long term results are available this situation is monitored by ATEC for future references.

The complete silo/filter unit is insulated. The mixed gas enters the silo with appr. 220°C and is cools down at the bottom of the silo to approx. 150°C due to false air entrance through the rotating discharge screw but still well above the acid dew point.

The rotating discharge screw is keeping the separated bypass dust in continuous motion (fluidized) and thereby avoiding sticking. Care has to be taken that the false air entrance through any silo opening especially the rotating screw is minimised to avoid moisture entering.ATEC has made several improvements on this system in the last realised projects and have found a good reliable working solution.

3.5 Bypass Dust Transport

The bypass transport is the only system were unexpected operational problems may occur. This is caused by sticking due to the hydroscopic nature of the salts contained in the bypass dust.

The transport of bypass dust is done mainly by pneumatic transport. Beyond a transport length of 200 m it is suggested to use pipe conveyor systems.

Based on the numerous bypass installations done by ATEC the following experiences have been made.

Bypass dust with a chloride content of 5% by weight (total salt content approx. 20%) is normally not causing problems in pneumatic transport systems. Up to 8% chloride content the sticking problems will increase. Further increase of chloride content may require the addition of raw meal to dilute the salt content.The transport air for the pneumatic transport is always dehumidified by air driers for this reason.


As the transport of bypass dust is critical to the reliable operation of the bypass systems over a longer period the design of such transport system is always done specifically for each plant installation.

3.6 Fan Equipment

Both fans, the cooling air fan and the main filter fan operate in a low dust atmosphere. Therefore no operational problems are usually experienced with those equipment.

The main filter fan is designed from the process point with a 10% reserve on volume and a 20% reserve on pressure.The clean air fan is designed with a 20% reserve on volume and a 40% reserve on pressure.This ensures sufficient capacity in case of required increased bypass rate and short term fluctuations.However the actual design capacity is always adapted to each system and reserve capacity may vary.

In case of power failure the shut off valve installed upstream of the quench chamber will close the mixed gas duct and protect the downstream equipment from excess heat. Further it is required that cooling air is blown into the quench for protection. This can be done by either having the cooling air fan connected to the emergency power system or have a smaller sized fan driven by an emergency generator installed.


3.7 Design Overview based on Lafarge Data

Below find an overview summarizing the process and design data for some of the possible alternatives for the main production data and equipment.

The process design can be adjusted quickly once Lafarge submits the relevant data detail basis data.

The options have been limited to the three bypass gas quantity given by Lafarge and for each of those system the process data for 250 g/Nm³ and 400 g/Nm³ of dust load.


4. PROJECT PROCEDURE AND TENDERING

As can be seen from the preliminary data given by Lafarge there are numerous alternatives which would have to be considered for a tender.

Additionally ATEC is always designing and adapting the bypass system to each specific plant layout and production situation. ATEC is therefore recommending the following steps to get the best technical solution at the most economic price.

a. Completing of a plant the basic engineering including - plant investigation - process flow sheet p- preliminary plant arrangement - technical specification of the main plant section and equipment- project planning- cost estimate

b. Based on this information Lafarge has the options to submit tenders for the detail engineering, supply, installation of the complete system with a single supplier or with individual suppliers.

ATEC is able to offer turnkey installation of bypass systems or to provide EPCM services (Engineering – Procurement – Construction Management) at either a fixed rate or for a fee of 12% of the purchase cost for the plant and equipment ATEC is to coordinate.

It has to be understood that for any plant and equipment procured by ATEC and resoled to our clients the overhead costs, risk rates and profits will be added.On the other side if ATEC is responsible for the technical coordination from process design to final commissioning and Lafarge is only placing the order with the supplier. Under this contract form no added costs except for the 12% management fee will be added.

ATEC managed contract procedure


In England ATEC has an agreement with the local company Fairport. Fairport is specialised in the detail engineering, supply and installation of equipment for the cement industry. ATEC has already completed successfully a turnkey contract for a bypass system at the Castle Cement plant in a consortium with Fairport. The contract was awarded in March 2005 and went into production in February 2006.

ATEC was responsible for

a. Process design for the complete plantb. Basic engineering for take off chamberc. Detail engineering for bypass dust cycloned. Process and equipment specification for the main plant and equipmente. Functional descriptionf. Supply of quench chamberg. Supervisory services during erection and commissioning

The remaining activities were completed by Fairport including civil engineering, civil works, electric and control system and complete installation.

Such an agreement does not exist with a French company for local contract work.

5. PROJECT PLANNING

The normal project period from award of contract until commissioning of the bypass system is 12 months.

If needed the contract period can be reduced to 9 months duration from clarification of all technical subjects until end of commissioning. However this can be achieved only if all design and engineering data are frozen (not changed) within the first week of contract start.

The usual tie in to the existing plant is limited to the take off chamber at the kiln riser and the connection of the clean gas duct to the main stack. These tie inn can be done anytime during the contract period in a 7 day period if properly planned by all involved parties including the plant personnel.The connections will be flanged off (blind flange). In case of the take off chamber the flange will be fitted with refractory lining.

The remaining plant and equipment can be installed during the plant operation. Removing of the blind flange and completing the connections will take 3 days only including cooling down of the relevant section.


6. ENCLOSURES

The above indicates the numerous alternatives and options to be considered in the design and engineering of bypass systems.

It is understood that Lafarge would also requires detail technical data and costing information for typical bypass installations and projects.

Therefore the following typical contract and tender information has been attached.

a. Tender for basic engineeringb. Completed contract documents for plant investigation, basic engineering

and supply of quench chamberc. Tender for a turn key installation at Lafarge Ciskoviced. Tender for engineering, supply and supervision at Lafarge Ciskovice

The client and plant data had to be removed from the enclosures “a” and “b” above as those do not refer to Lafarge plants.

We hope this information assists you in your project planning. If you need any further information, do not hesitate to contact us.

With best regards,

_______________________ _______________________Dr. Günther Schwaiger Wilfred Zieri

Managing Director Sales ManagerA Tec GmbH A Tec GmbH

bypass systems

Documents