METALURGIA INTERNATIONAL by mercy2beans119

VIEWS: 296 PAGES: 4

									METALURGIA INTERNATIONAL                                                                                                                .



 RECLAMATION SYSTEM FOR RECYCLING OF CHEMICAL BONDED SAND WASTE
                     INTO FOUNDRY INDUSTRIE

   Prof.dr.eng. Ioan MARGINEAN - Politehnica University of Bucharest, Dr. Eng. Carmen DUMITRU - INTEC SA
    Bucharest, Prof. Dr. Eng. Aurel CRISAN- Transilvania University of Brasov, Prof. dr.eng. Viorel DAN Viorel –
                      Technical University of Cluj, Eng. Gheorghe TOADER – UTTIS SA Bucharest
====================================================================================
Key words: sand waste, recycling, reclamation


Abstract: The paper present the authors research to develop a new concept of reclamation system that has as an important
component a filtration and neutralisation module. The authors justify the importance of thermal processing of sand waste by
technological and ecological point of view.

                    1. INTRODUCTION                                   - Thermal reclamation by burning of binding film, in special
                                                                      equipments,
     In the context of existence of a more striking competition       - Bacteriological reclamation by reducing the phenol contain in
pressure on the castings market, castings producers all over the      waste,
world manifest a clear tendency to fall in to a high technological    - Re-use of sand waste, without processing in the following
level, capable to assure simultaneous a high dimensional              direction: use as road rambling (for sand waste which contain
precision, o good surface quality, a reproducible casting             less for 1 mg phenol/Kg waste); use to fabrication of product
characteristics and a high productivity.                              based on hydraulic binders (for sand waste which contain less
     The foundry industry faces the necessity to correlate the        for 5 mg phenol/Kg waste); use in fabrication of some product
need to increase quality with that of observing the                   which need processing methods capable to destroy organic
environmental conditions imposed through an increasingly              binder no mater the phenol contain (fabrication of bricks,
tough legislation and, not last, with the need of maintaining         cements, etc.)
competitiveness through the providing of high quality at low               Used sand waste reclamation it isn’t, in self, a new solution
execution prices. The need to improve the quality of the cast         but it acquires a new dimension based on used binder systems
parts favoured the expanding of the use of binding systems            evolution, which dictate a continuous adaptation of processing
based on synthetic resins, which can simultaneously ensure            technologies to the binder intrinsic characteristics.
quality, productivity and competitive price, but brought about             In the present are known four methods for sand waste
the problem of large refractory material consumption and of           reclamation: dried; wet, mechanical and thermal, plus
storing certain chemically active waste.                              combinations. Selection of optimal reclamation technology to
     The level of waste coming from the foundry industry is           be used in a specified foundry is made as a function of cast
considered to be at present de approx. 1 tone of waste/1tone of       metal, used binder and recycling option. Based on these four
cast parts, 66-88% of them being represented by used forming          reclamation method it was developed complex systems for
mixtures, mostly chemically bound with resins from the                reclamation and recycling of sand waste. These systems
category of the phenolic, phuranic, phenol-phormaldehidic             assume:
types, etc. Unlike the raw forming mixtures based on inorganic        - taking over of sand after mould crash,
natural binders (clay and bentonite), in case of chemical             - processing for the purpose to bring to the granule shape,
bonding with synthetic resins, the entire used mixture goes to        - Thermal, mechanical or mechanical-thermal treatment of sand,
the waste dump after only one use, always having a high               to eliminate the binder film residue and the impurities,
residual resin content. The resins used in foundries are mostly       - Separation of grain component,
phenolic. The phenol is one of the substances considered,             - taking of protection measure against pollution, consist in
according to the environmental legislation, as especially             special filters capable to retain dust and pollution substance.
dangerous because it is easily dissolved by the meteoric waters,           Reclamation systems with a large utilization at the moment
it reaches the phreatic layer and pollutes the entire ecosystem       are the attrition unit. In attrition units the temperature is low and
for kilometers around the source.                                     refractory material recuperation is 75…90%. These systems can
     Under these circumstances, the need appeared in the              be used, with some limits, for chemical bonded sand
foundry industry to improve its forms performing technologies         reclamation, too.
through the usage of more productive binders which provide a               Attrition units can’t assure a total clean of the binder film
higher quality for the foundry items, brought about the issue of      based on chemical binder systems as synthetic resins. After a
environmental norms non-observance.                                   number of reclamation the binder accumulations into the mould
     As a consequence, the foundry industry is put in situation to    structure lead to exceeding the binder acceptable technological
look for solution for the pollution problem caused by the sand        limits. As a consequence the mould sand pollution capacity is
waste storage for the purpose to participate to the European          growing (high emission of SOx, NOx, N and HxCy) and the
community effort to reduce industrial pollution and to achieve a      castings quality is affected in negative way (exogenous
good natural resources management. For to reach these                 sulphurs, sulphur and nitrogen diffusion in the superficial layer
objectives there is in the present four main directions for action:   of casting).
- Mechanical reclamation by attrition,                                     The dust that result after processing in attrition unit has a
                                                                      high binder concentration and can’t be stored because it will
METALURGIA INTERNATIONAL                                                                                                           .
introduce in the ecosystem the same binder quantity as to an        - sand processing for the purpose to bring to the granule shape,
usual chemical bonded sand storage.                                 - thermal treatment of sand, to eliminate the binder film residue,
    That means that mechanical reclamation without binder           - taking of protection measure against pollution, consist in
neutralizes isn’t a proper solution for protection against          special filters capable to retain dust and pollution substance.
pollution in case of chemical bonded sand. The better                   The processing diagram for the reclamation system is
reclamation solution in case of chemical bonded waste sand is       presented in figure 1.
thermal reclamation.

  2. TECHNOLOGICAL RECLAMATION FLOW
              OF SAND WASTE

     A technological flow for thermal reclamation of sand waste
is composed by the following stages:
- Mechanical processing of chemical bonded waste sand for the
purpose to Break the lumps; put the sand into grain shape and
cleaning of ferrous and non-ferrous impurity;
- Thermal processing of sand grain for the purpose to burn the
binder films;
- cooling of reclaimed sand to the ambient temperature;
- Filtration and neutralise burning gases resulted from the
thermal processing process.
     The main component of technological flow is the thermal        Fig. 1 The principle scheme of reclamation system
processing. This is achieving in a fluidised bed roasting           1 Lamp breaker, 2.-Transportaton band with magnetic releasing;
equipment.                                                          3 – Upright transportation; 3 – Storage and dosage system;
     There are two reasons why fluidisation is used:                4-Fluidised bed roaster, 5-Exhausting system; 6-Fluidised bed
- It assure an intense heat transfer by radiation from he heating   cooler
source to the refractory material;
- It provides a higher oxygen concentration, needed for burning          It can be seen that the thermal regeneration line for sand
of binder films;                                                    waste has the following general structure:
     There are three technological way for thermal processing of    - Pre-reclaimed equipment which produces lump broken and
sand into fluidised bed roasting equipments.                        rating of granular material;
     In a first technological way, used in low capacity             - Equipment for vertical transportation of granular material
equipments, the equipment just made burning of grain sand. In       - Storage silo for pre-reclaimed sand;
this type of equipment refractory material came directly into       - Burning equipment in fluidised bed;
roasting chamber. With the help of burners placed on the            - Cooling equipment for the reclaimed sand regenerated;
bottom of the chamber is simultaneous achieve both fluidisation     - Filtering equipment for the gas resulted from the burning
and ignition of processed material.                                 process;
     Sand fluidisation is made with burning gases and air with      - Silo for reclaimed sand.
the proper pressure. Because of specific thermo-destruction              In figure 2 is presented the equipment of thermal
mechanism of binder film in case of synthetic resins, in which      reclamation sand end in figure 3 is presented the fluidised bed
inflammable compounds is produced, binder films present to the      burning and cooling equipments.
refractory grain surface ignite and burn. This type of equipment
has a lower processing temperature of just 677°C.
     In the second technological way the equipment achieve both
pre-heating and roasting of grain material. The processing
equipment has two chambers: pre-heating chamber positioned
on the top and roasting chamber positioned on the bottom. The
temperatures recommended for thermal reclamation in this case
are 800°C into roasting chamber end 300°C into pre-heating
chamber. In both chambers sand is in fluidised state.
     The third technological way is the most complex and is
applied to the high productivity equipments. In this case the
equipment achieves preheating, roasting and cooling of grain
material. The processing equipment is build with three
chambers: heating chamber (on the top), roasting chamber (in
the middle), and Cooling chamber (on the bottom). In this
equipments are simultaneous three distinctive sand ration
positioned into the three processing chamber. The specific
working temperatures of the equipment are 300°C into pre-
heating chamber, 677°…800°C into roasting chamber end               Fig. 2 The thermal reclamation equipment
30°…600°C into cooling chamber.
     Based on presented reclamation method it was developed a           The novelties element of reclamation system, proposed by
complex systems for reclamation and recycling of sand waste.        the authors, is the filtration and neutralization module for the
These systems assume:                                               gases resulted from binder film burner in the roasting
- taking over of sand after mould crash,                            equipment.
METALURGIA INTERNATIONAL                                                                                                                                                                         .
                                                                                                        This module makes the fallowing processing operation:
                                                                                                    Undusting of the burning gases; Cooling of gases; Filtration by
                                                                                                    special filers; Gas filtration by an active carbon column for the
                                                                                                    purpose to neutralise them. The process diagram is presented in
                                                                                                    figure 5.


                                                                                                           Burning gases +                             Undusting                   Cooling at
                                                                                                                Dust                                                                 50°C


                                                                                                                                                                               Fine Dust
                                                                                                           Cool Air                          Gases at
                                                                                                                                                                                particle
                                                                                                                                             50°C
                                                                                                                                                                               filtration


                                                                                                                        Gases at 25°C                             Active carbon column



                                                                                                                                                       Clean air
                                                                                                                        Fig. 5 The filtration and neutralisation process diagram

                                                                                                        To demonstrate the efficiency of solution was made
                                                                                                    measurement of the CO, NOx, CO, SO2 and COV content in
                                                                                                    burning gases, before and after neutralization module. The
                                                                                                    result are presented in the figures 6, 7 and 8.


                                                                                                                        70
   Fig. 3 The fluidised bed burning and cooling equipments.                                                             60
                                                                                                                        50
                                                                                                      T im p , se c .




    It is already known than the burning gases resulted from                                                            40
destruction of synthetic binders as synthetic resins have a high
                                                                                                                        30
concentration of volatile organics compounds.
    The experimental research made on mould thermo-                                                                     20
destruction put in evidence the main harmful emissions, as it                                                           10
presented in the figure 4. Release of these gases in the                                                                 0
atmosphere is in contradiction with the environmental                                                                        1   2   3   4    5    6     7    8    9   10 11 12 13 14 15
protection.
                                                                                                                                                         NO, ppm

                              0.1                                                                                                    Continut in gazele de ardere la iesirea din calcinator
                                                                                                                                     Continut in gazele de ardere la iesirea din neutralizator
                             0.09

                             0.08                                                                   Fig. 6 Comparation between NO concentrations in the burning
                             0.07
                                                                                                    gases before and after neutralisation module
     lb/tone of cast metal




                             0.06

                             0.05                                                                                       70
                                                                                                                        60
                             0.04
                                                                                                                        50
                                                                                                      T im p , s ec .




                             0.03
                                                                                                                        40
                             0.02
                                                                                                                        30
                             0.01
                                                                                                                        20
                               0                                                                                        10
                                                                          Toluene
                                             Benzene



                                                       Aniline




                                                                                    Methilaniline
                                    Phenol




                                                                 Cresol




                                                                                                                         0
                                                                                                                             1   2   3   4    5    6     7    8    9   10 11 12 13 14 15
                                                                                                                                                         NOx, ppm
Fig. 4 The main ten categories of harmful emissions in the
synthetic resin thermo-destruction                                                                                                   Continut in gazele de ardere la iesirea din calcinator
                                                                                                                                     Continut in gazele de ardere la iesirea din neutralizator
    The authors propose that this problem to be solved by
including in the reclamation system of a filtration and                                             Fig. 7 Comparation between NOx concentrations in the burning
neutralization module.                                                                              gases before and after neutralisation module
METALURGIA INTERNATIONAL                                                                                                                                      .
    As it can be seen in the figure 6 and 7 the burning gases has                              - Eliminating waste storage charges that include special storage
a smol percent of NO and NOx and this is adsobed by the active                                and transportation fees.
carbon column.
    SO2 emision, mesured in burning gases is higher then NO                                                         4. CONCLUSIONS
and NOx (to be seen figure 8) because SO2 is one of
decomposition compound.                                                                            The reintroduction in the industrial circuit of sand waste is
    By passing trough active carbon column, the content of SO2                                now a priority direction of the effort policy enforcement for the
in burning gases is reduced, which demonstrate that the                                       conservation of global environment.
proposed solution is viable.                                                                       The large extend of chemical binder using, conduct to an
                                                                                              advanced environmental pollution in the area where are placed
                                                                                              foundries. Finding of new technical solutions for this problem
                     70                                                                       is justified by chemical pollution produced by nonconforming
                     60                                                                       storage of sand waste and by high input of refractory materials
                     50                                                                       in the foundry industrie
  T i m p , se c .




                                                                                                   In this context the issue of introducing of reclamation
                     40
                                                                                              systems in small and medium foundries represents a necessity.
                     30                                                                       Because they allow them to fall in to quality standards
                     20                                                                       demanded by the market and to situate them in requirements for
                     10                                                                       costs and environmental protection.
                     0
                                                                                                   The modul for neutralise the volatile organics compounds
                                                                                              from the burning gases represent a novelty in the domain end
                          1   2   3   4    5    6    7     8    9   10 11 12 13 14 15
                                                                                              can be a solution for the problem of environmental medium
                                                     SO2, ppm                                 protection in case of thermal reaclamation units.
                                                                                                   By attain of a reclamation system functional in terms of
                                  Continut in gazele de ardere la iesirea din calcinator      reduced productivity, adaptable in small series foundries,
                                  Continut in gazele de ardere la iesirea din neutralizator   authors proposed and succeeded in creating a premises for
                                                                                              assimilation of a top techniques in a field of great actuality.
Fig. 8 Comparation between SO2 concentrations in the burning                                       The reclamation of chemical bonded sand waste contributes
gases before and after neutralisation module                                                  to a better management of natural resources, ensures
                                                                                              environmental protection towards the harmful attack of the
    To confirm this result in case of organic volatile compound                               waste dumps for storing the forming mixtures with polluting
it was made a cromatographique analise on the same samples.                                   chemical substances content and it contributes, through the
It was confirmed that by point of vue of composition, in the                                  prevention of pollution, to the improvement of public health in
burning gases are predominant aromatique hidrocarbure. This                                   the areas affected by the vicinity with industrial platforms in the
has a 90% proportion.                                                                         field of foundry.
    The main hidrocarbures determined in the composition of
gases that result from decomposition of resin binder are phenol
                                                                                                                    4. REFERENCES
and benzene.
    Cromatopgrphique analise indicate a sensible lower content
                                                                                              [1 J. Danko, s.a. – Reclamation of used sands in foundry
of     organic volatile compounds in the gas samples after
                                                                                              production, Metalurghia, 42 /2003 p. 173-177
neutralization by passing trough active carbon column.
                                                                                              [2] M.C. Mac Combe – Progres des moyens de regeneration du
                                                                                              sable, Hommes et Fonderie, mai, 1997
                       3. TERMS OF REINTRODUCTION OF                                          [3 Pierre Druel – Recyclage total du sable a l’Acierie et
                      RECLAIMED SAND IN THE MOULDING                                          Fonderie de la Haute Sambre a Berlaimont - Hommes et
                              EXECUTION FLOW                                                  Fonderie, mai, 1997
                                                                                              [4] Philippe Marin – Regeneration de sable de fonderie aux
    Thermal reclamation presents the following important                                      Fonderie d’Ussel - Hommes et Fonderie, mai, 1997
characteristics by point the view of reuse conditions:                                        [5] *** La regeneration de sable de decochage s’amortit en
- The degree of reuse of the sand is 90%…100%                                                 deux ans – ou moins- avec une installation Simpson ProClaim
- Reclaimed sand is more stable in terms of heat than the new                                 de National Engineering
one, which directly affect, in positive way the quality of cast                               [6] G Muller s.a Oko-Sandregenierung, Giesserei Praxis nr
parts.                                                                                        11/12, 1994, p.308-310
- Reclaimed sand can be used to make mould with all type of                                   [6] ***Regeneration thermique de sables a vert et chimique
binders.                                                                                      dans une fonderie Italiene, Fonderie Fondeur d ‘Aujourd’hui,
    The processing reclamation conditions make possible, as                                   aug-sept. 1993, p. 12-15
effect of rounding the grain and filling of existing hollows and                              [7] *** Thermal decoring and reclamation plant for cold-box,
cracks into grain, decreasing of binder proportion necessary for                              hot-box and shell moulding sands, Casting Plant and
execution of a mould sand with similar characteristics similar to                             Technology International 3/1999
that achieved with new sand.                                                                  [8] *** Reclamation of foundry sand using natural gas – Centre
    The reintroduction of reclaimed sand in the moulding flow                                 for the Analysis and Dissemination of Demonstrated Energy
has as consequence the following economic advantages:                                         Technology
- Reducing costs of acquisition, transport, storage and handling                              [9. Pichouron – Regeneration collective de sables en Europe,
of refractory materials;                                                                      Fonderie d ‘Aujourd’hui, febr. 1994, p.18-21
- Reducing the cost of performing of cast moulds by reducing                                  [10]*** Calcifire – Sand Reclamation Technology,
the costs of raw materials (sand and binder);                                                 www.mindfully.org

								
To top