Faculty of Chemical Engineering and Technology University of Zagreb in cooperation with
Hrvatske vode, Legal entity for water management (HR) Department of Civil & Environmental Engineering, College of Science, Engineering and Technology, Jackson State University (USA) Croatian American Society (HR) Slovenian Biomass Association (SLO) ODRAZ, Sustainable Community Development (HR)
3rd International Symposium on Environmental Management Towards Sustainable Technologies
Conference Proceedings October 26 - 28, 2011 Faculty of Chemical Engineering and Technology, Zagreb, Croatia
Sponsored by:
CONFERENCE PROCEEDINGS of SEM2011
Publisher: Faculty of Chemical Engineering and Technology, University of Zagreb, Marulićev trg 19, 10000 Zagreb, Croatia Phone: +385 1 4597 281, Fax: +385 1 4597 260, E-mail:
[email protected]
Editors: Natalija Koprivanac, Hrvoje Kušić and Ana Lončarić Božić
Logo: Edi Murgić
A CIP catalogue record for this book is available from the National and University Library in Zagreb under 780938 ISBN 978-953-6470-56-3
Organized by: Faculty of Chemical Engineering and Technology, University of Zagreb in cooperation with
Hrvatske vode, Legal entity for water management (HR) Department of Civil & Environmental Engineering, College of Science, Engineering and Technology, Jackson State University (USA) Croatian American Society (HR) Slovenian Biomass Association (SLO) ODRAZ, Sustainable Community Development (HR) Under the auspice of: Croatian Parliament; Ministry of Environmental Protection, Physical Planning and Construction; Ministry of Science, Education and Sport; Ministry of the Sea, Transport and Infrastructure; Ministry of Environment and Spatial Planning of Kosovo; Office for Sustainable Development of Monte Negro; University of Zagreb; University of Split; Croatian Academy of Engineering; Croatian Environment Agency; Environmental Protection and Energy Efficiency Fund; Croatian Chamber of Economy; American Chamber of Commerce in Croatia (Green Building Council); Croatian Business Council for Sustainable Development; Energy Institute Hrvoje Požar; The Institute of Economics, Zagreb; The Croatian Association of Engineers; Croatian Society of Chemical Engineers; Croatian Chamber of Architects; District of Cazin (BIH) Scientific and Organizing Committee President: Natalija Koprivanac Roko Andričević, Anđelka Bedrica, Felicita Briški, Besim Dobruna, Neven Duić, Mark Gero, Zlata Hrnjak-Murgić, Tonka Kovačić, Savka Kučar-Dragičević, Dragan Kukavica, Stanislav Kurajica, Hrvoje Kušić, Stjepan Leaković, Danuta Leszczynska, Ana Lončarić Božić, Nenad Mikulić, Ljubomir Miščević, Zoran Nakić, Lidija Pavić-Rogošić, Gordana Pehnec-Pavlović, Davor Romić, Suad Rošić, Nenad Smodlaka, Siniša Širac, Martina Šumenjak, Vesna Tomašić, Branko Tripalo, Đurđa Vasić-Rački
International Scientific Advisory Board Prof. Dr. I. Balcioglu (TUR), Prof. Dr. F. Bašić (HR), Prof. Dr. M. C. Cann (USA), Prof. Dr. D. D. Dionysiou (USA), Prof. Dr. S. Esplugas (ESP), Dr. F. Evers (NED), Prof. Dr. M. Giaoutsi (GRE), Prof. Dr. P. Glavič (SLO), Dr. C. Hey (GER), Prof. Dr. M. Hraste (HR), Dr. Lj. Jeftić (HR), Prof. Dr. M. Kaštelan-Macan (HR), Prof. Dr. V. Kaučič (SLO), Prof. Dr. B. Kunst (HR), Prof. Dr. J. Leszczynski (USA), Prof. Dr. A. Magerholm Fet (NOR), Prof. Dr. A. Majcen Le Marechal (SLO), Prof. Dr. M. Metikoš-Huković (HR), Prof. Dr. P. Novak (SLO), Prof. Dr. G. Li Puma (UK), Prof. Dr. M. Schreurs (GER), Prof. Dr. M. Scoullos (GRE), Dr. S. Švaljek (HR), Dr. V. Vađić (HR), Prof. Dr. G. Varallyay (HUN), Prof. Dr. D. T. Waite (AUS), Prof. Dr. T. Winnicki (PL)
- 158 CALCIUM SULPHOALUMINATE ECO-CEMENT FROM INDUSTRIAL WASTE Neven Ukrainczyk1*, Nirvana Franković Mihelj2, Juraj Šipušić1 1
Faculty of Chemical Engineering and Technology, University of Zagreb, Marulićev trg 19, 10000 Zagreb, Croatia 2 Environmental Protection and Energy Efficiency Fund, Ksaver 208, HR-10000, Zagreb, Croatia *e-mail:
[email protected], tel: +385 1 4597 228, fax: +385 1 4597 260
Abstract The manufacture of portland cement (PC) consumes huge amount of energy and has a significant CO2 emission. Calcium sulfoaluminate cement (CSAC) is a promising alternative binder to PC due to: a) lower limestone requirement in CSAC; b) about 200 K lower sintering temperature for CSAC than for PC; and c) much easier grinding of the fired CSAC. Each of these arguments considerably reduces energy consumption and CO2 emission from cement manufacture. In this paper, the potential benefits offered by CSAC production from industrial wastes or byproducts already present in Republic of Croatia had been addressed. A variety of industrial wastes, namely phosphogypsum (PG), coal bottom ash (BA) and electric arc furnace slag (EAFS), were used as raw materials to provide additional environmental advantages in production of CSAC. Mass fraction of Klein’s compound (the principal hydraulic mineral) in the prepared CSAC was determined by quantitative X-ray powder diffraction. In conclusion, CSAC production offers an alternative and feasible way of industrial waste minimization. Keywords: calcium sulfoaluminate special cement, X-ray powder diffraction, waste minimisation, phosphogypsum, electric arc furnace slag, coal bottom ash 1. INTRODUCTION Man-made CO2 emissions and extensive use of natural resources pose a serious threat to the future sustainable development and also trigger climatic change. Cement industry accounts for up to 7% of CO2 emissions due to the large global production of cement (2 billion tones per year) and also due to the high temperatures involved in production along with large quantity of calcareous materials needed per tone of cement produced. However, the cement industry has a large potential of reuse of vast quantities of various industrial wastes and by-products that can be incorporated, in certain amount, as raw material or added during the final grinding of clinker. Calcium sulphoaluminate cement (CSAC) had been recognized as the so called “low energy cement” due to the much lower energy consumption for its production and is therefore extensively investigated in recent years [1]. At same mixing water to cement ratios and achieved degrees of hydration the obtained porosity of cement pastes made from CSAC is considerably lower than that of ordinary PC. This is because of the higher stoichiometric requirement of the chemically bound water in the hydration products formed by hydration reactions of CSAC, especially in that of the AFt type [1] hydration products. About million tons of CSAC type cements are produced annually in China [2], where special cement standards were issued. To manufacture CSAC clinker, an appropriate starting raw mixture need to be burnt at maximum temperatures 1200-1300°C. The reuse of such waste raw materials, principally phosphogypsum, reduces both the temperature and the time of the firing process (e.g. [3]). On a large scale manufacture, the firing process can be performed in conventional rotary kilns used for PC manufacture [4]. Kleinite (4CaO·3Al2O3·SO3 i.e. C4A3s in shortened cement mineralogy notation, Table 1) is the principal mineral phase responsible for the early strength development during cement hydration. Depending on the proportion of the individual mineral phases in the clinker and the content of calcium sulphate, CSAC may perform as non-expansive high early strength cements, or as expansive cements. This depends on the time of formation of ettringite: before (no expansion) or after (expansion) the development of the rigid skeletal structure. To prevent expansion, the ettringite must be formed in the absence of free CaO [1]. However, a limited amount of CaO is desirable in order to enable rapid strength development and a high early strength. The optimal C4A3s content in non-expansive CSAC is between 30 – 40% [3]. In the presence of the iron minerals in the raw mixture, a considerable amount of iron may form solid solution of the type C4A(3-x)Fxs where x Proceedings of SEM2011, Oct 26 – 28, Faculty of Chemical Engineering and Technology, Zagreb, Croatia
- 159 may be up to 0.15 [5]. The ferrite phase (C2(A,F)) exhibits a higher reactivity than in ordinary PC, contributing to both the early strength development and long term strength of the CASC. This higher reactivity is most likely due to its formation at lower firing temperature [5]. The C2F starts to be formed at about 1100 °C and at higher temperatures it incorporates alumina, which finally attains a composition of C6AF2. To obtain the kleinite (C4A3s) and to avoid its decomposition as well as decomposition of CaSO4 at higher temperatures, the firing temperature in the manufacture of CSAC must not exceed 1300°C (especially if reusing the waste as raw materials). Belite (C2S) is usually present in its β modification, but also sometimes in α form. Belite has only very small contribution to early strength development, but is mainly responsible for the ultimate strength of the CASC. Ternesite (C5S2s, also called sulfospurrite) can be formed as an intermediate phase, from about 900 °C [3] and decomposes above 1200-1280 °C to C2S and CaSO4. In this work, the potential benefits offered by CSAC production from industrial waste materials already present in Republic of Croatia had been addressed. The main raw material components are: waste phosphogypsum form mineral fertilizer production, electric arc furnace slag (EAFS) form steel production and bottom ash from coal fired electric energy production plant. The quantity of bauxite and limestone are added to the raw mix in order to correct bulk chemical and mineralogical composition to obtain useful properties of the final CSAC cement. Mineralogical composition of samples was investigated by XRD powder diffraction. 2. ELABORATION 2.1. CASC vs. PC: Assessment of Energy Saving and CO2 Emission CSAC can lay claim to being a very attractive ‘‘high-performance’’ cement mainly due to following reasons [1]: a) the low energy and low CO2 emission associated with its production; b) its ability to form cements, mortars and concretes with high early and final strengths; c) shrinkage compensating abilities; d) its excellent durability, especially in saline marine environments, and the protection it affords to embedded steel (as well as excellent resistance to alkali-silica reaction [1]). Whereas OPC is normally interground with a few weight percent of CaSO4 (or Cs in cement notation, Table 1), CSAC is typically interground with 16–25% of CaSO4. Next, the energy requirement and environmental impact of CASC and PC production is quantitatively compared. The energy balances and CO2 emissions depend on the efficiency of the kiln and fuel. Indications of these balances are shown in Tables 2-4, regarding firing process, grinding process and CO2 emission. For the purpose of such comparison we consider a standard grade PC product (CEM II/B-M(S-V) 42,5N) with 15 mas. % of supplementary addition (granulated blast furnace slag and fly ash). On account of the low CaCO3 content, relative to OPC, CO2 emissions are markedly reduced in CSAC clinkers. Further economical benefits of CASC over PC in specific fuel (per kilogram of cement produced) and CO2 release results from the high level of gypsum addition, 15–25%, typically made to the clinker, as well as the low energy requirements for grinding the clinker. The influence on the energy requirement for the firing in kiln was divided in two segments (Table 2): (i) the influence of the firing temperature, and (ii) the influence of the amount of raw material. Literature values were used for firing temperature and amount of raw material [1] for both types of cements. Enthalpy of the formation of the CSAC clinker is much lower than that of ordinary PC and even of belitic clinkers. Firstly, this is mainly because the thermal losses are reduced due to a lower firing temperature required (1200 - 1300 °C instead of 1450 °C). Secondly, energy saving for firing is also due to the lower overall CaO content to be produced in CSAC, and because the fraction of the CaO is formed from CaSO4 instead of CaCO3. A potential problem in industrial manufacture may be the partial thermal decomposition of CaSO4 during firing the raw material, which may call for an appropriate technology to control the SO3 emission. However, the emission of CO2 and NOx is significantly reduced [6]. The energy requirement for the grinding process of the CSAC clinker is much lower than that of typical ordinary PC clinker (Table 3). The values in Table 3 show energy savings assessment in grinding process of raw materials (before sintering) as well as cement clinker (after sintering). According to the known stoichiometric amount of the raw materials that needs to be grinded the savings in energy is estimated to be about 28 %, while the overall savings is estimated to be about 33 %. Table 4 presents the ecological and economical benefits of CASC over PC regarding the CO2 emission. The basic fee for CO2 emission in Croatia was taken to be 14 - 18kn/t CO2. Reaction of CaCO3 decomposition (CaCO3 → CaO + CO2) forms 44 mas. % of CO2. The emission of CO2 per t of cement is Proceedings of SEM2011, Oct 26 – 28, Faculty of Chemical Engineering and Technology, Zagreb, Croatia
- 160 calculated according to the amount of the CaCO3 raw material needed for the production of cement. For PC this emission amounts 0.374 t CO2 / t cem. (0.85 CaCO3 / t cem. ⋅ 0.44), while for CSAC the savings is 0.242 t CO2 / t cement (Table 4). Beside the CO2 emission from CaCO3, there is also a significant emission resulting form fuel combustion. According to Cement data book by W.H. Duda, value for energy requirement for 1 t of cement and amount of CO2 emission in kg / GJ the estimation of emission from fuel combustion is calculated (e.g. for CSAC 2.48 GJ / t cem. ⋅ 90 kg CO2 / GJ = 223 kg / t cem). The waste management savings assessment is given in Table 5. Table 1. Cement mineralogy notation Oxides
CaO
Al2O3
SiO2
SO3
Fe2O3
H2O
MgO
TiO2
Symbol
C
A
S
s
F
H
M
T
Table 2. Firing process: ecological and economical benefits of CASC over PC SINTERING
CSAC
PC (CEM II)
Savings in regard to the PC
Temperature
1200 °C Lower heat loss
1450 °C (3.1 GJ/t cem)
~15 % (0.5 GJ/t cem)
0.3 t CaCO3 / t cement
0.85 t CaCO3 / t cement
1.25 t raw / t cement
1.6 t raw / t cement
Amount
Total saving
0.55 t CaCO3 / t cement => 0.6 GJ/t* 0.35 t raw / t cement > 1.1 GJ/t cem
*
considering 60% of energy for CaCO3 decomposition (1.78 GJ/t CaCO3) for conversion to per t of cement
Table 3. Grinding process: economical benefits of CASC over PC GRINDING
CSAC
PC (CEM II)
Savings in regard to the PC, %
raw materials for sintering
0,3 t CaCO3 / t cement bauxite 10 %
0,85 t CaCO3 / t cement (16 kWh / t cem.)
~ 28*
of cement klinker
sintered = low energy requirement ~ 40 % less than for PC
partly melted = huge energy requirement (36 kWh/ t cem.)
~ 40
Total saving
~ 33
*economical benefit for the same specific energy requirement (per 1t cement) for grinding due to lower mass of raw materials for production of 1t of cement.
Table 4. CO2 emission: ecological and economical benefits of CASC over PC CO2 EMISSION
CSAC
PC (CEM II)
Savings in regard to the PC, %
Raw material (CaCO3)
0.3 t CaCO3 / t cement 0.132 t CO2 / t cement
0.85 t CaCO3 / t cement 0.374 t CO2 / t cement
0.242 t CO2 /t cement
FUEL
(2.48 GJ/t cem.) 90 kg CO2 /GJ 223 kg CO2 / t cem.
(3.1 GJ/t cem.) 90 kg CO2 /GJ 279 kg CO2 / t cement
20 %
Total saving
42.5 %
Proceedings of SEM2011, Oct 26 – 28, Faculty of Chemical Engineering and Technology, Zagreb, Croatia
- 161 Table 5. Waste management: savings assessment. PC (CEM II) Savings in regard to the PC, %
CSAC
bottom ash ~ 12 % EAFS ~ 30 % phosphogypsum ~ 15 % (35 kn/t waste) 14.7 kn/t cement
ash + EAFS = 10 % (35 kn/t waste) 3.5 kn/t cement
11.2 kn / t cem.
Table 6. Chemical composition of used raw materials (in mass %). Fe2O3 CaO MgO MnO TiO2 Na2O + K2O SiO2 Al2O3
SO3
EAFS
11
2
30
33
13
6
-
-
-
coal bottom ash
54
23
7
5
-
-
-
-
-
bauxite
3.5
57
22.5
1
0.5
-
2.5
