Optimization of Steel and Methanol Production in an Integrated

Transcription

1 Optimization of Steel and Methanol Production in an Integrated H. Ghanbari, H. Helle, M. Helle, F. Pettersson and H. Saxen Åbo Akademi University Heat Engineering Laboratory Åbo / Turku, Finland tel hamid.ghanbari@abo.fi 1

2 Introduction 1 Energy saving is an important issue in the steel industry. Improvement of the energy efficiency, to reduce the energy consumption, will increase the economic profitability as well as reducing the environmental impacts. Steel plants have a significant contribute to the global CO 2 emission: 4-6% of man-made CO 2, largest point source of CO 2 in the world, Blast Furnace Ironmaking is responsible for % of this emission, 2

3 Introduction 2 According to ULCOS: CO 2 issue is a business risk for the Steel Industry in Europe Cost Acceptance by society Potential Direction: New Technologies New Reductant and fuels; focus on biomass Process Integration; by-products and CO 2 Capture and Storage Most of the high value Off-gases from different units such as Coke Oven Gas (COG), Blast Furnace (BF) and Based Oxygen Furnace (BOF) are used in Combined Heat and Power plant which is not the most efficient way to use them. 3

4 Introduction 3 MeOH as a FUEL MeOH production from natural gas or biomass resources Several commercial technology to produced MeOH from COG in china e.x. Shanxi Tiianhao chemical company Ltd (first plant, 2005); production of tons per year. 4

5 Models of the Unit Process and Emissions 1 CP: coke-making plant, SP: sintermaking plant, ST: hot stoves, CS: CO2 stripping unit, BF: blast furnace, BOF: basic oxygen furnace and PP: power plant. 5

6 Models of the Unit Process and Emissions 2 Blast Furnace Model: Input and output variables and their constraints, as well as sinter and coke mass production rate constraint. Treatment of the Gas Preheating State Hot Stoves Comp. State NO. 1 TGR+BL* TGR+BL State NO. 2a BL TGR+BL State NO. 2b BL(No TGR) BL(No TGR) State NO. 3 TGR TGR+BL State NO. 4** TGR TGR *Bl: Oxygen Enriched air **State No. 4: pressuerized Cold Oxygen 6

7 Models of the Unit Process and Emissions 3 Coke Plant: Linear relations between the mass flow rate of feed coal and the mass flow rate of coke and volume flow rate of (purified) coke oven gas (COG) are assumed m coke 0.695m coal ; V COG 319.7m coke 3 m n t Sinter Plant: Only the raw materials iron ore, coke and limestone are considered, and in addition to them, the recovered heat is also taken into account, i.e., m sint 1.042m ore, m coke,sint m sint; m lime,sint m sint; Q sint m sint MJ t which gives the (internal) flow rate of coke available for the blast furnace: m coke, int m coke m coke, sint Hot Stoves: The strongly oxygen-enriched blast and the recycled and CO 2 -stripped top gas are compressed and then heated in the hot stoves, which are assumed to operate as a single continuous counter-current heat exchanger in steady state with the heat transferred from burning oil. 7

8 Models of the Unit Process and Emissions 4 Basic Oxygen Furnace: The mass flow of liquid steel and the volume flow rates of oxygen to and off-gases from the BOF are given as function of the mass flow of hot metal (hm); 3 m n m ls 0.895m hm m scrap ; V O,BOF 45.6 m hm ; V BOF 41.5m 2 t hm 3 m n t CHP plant: overall energy balance between residual of gases from BF and part of the BOF are used to produce electricity and district heat. E pp =(1-β-М)V BF H BF +k V BOF H BOF P PP. E ; Q 1 E PP 8

9 Treatment of the Gas Preheating Coke Plant: Linear relations between the mass flow rate of feed coal and the mass flow rate of coke and volume flow rate of (purified) coke oven gas (COG) are assumed m coke 0.695m coal ; V COG 319.7m coke 3 m n t Sinter Plant: Only the raw materials iron ore, coke and limestone are considered, and in addition to them, the recovered heat is also taken into account, i.e., m sint 1.042m ore, m coke,sint m sint; m lime,sint m sint; Q sint m sint MJ t which gives the (internal) flow rate of coke available for the blast furnace: m coke, int m coke m coke, sint Hot Stoves: The strongly oxygen-enriched blast and the recycled and CO 2 -stripped top gas are compressed and then heated in the hot stoves, which are assumed to operate as a single continuous counter-current heat exchanger in steady state with the heat transferred from burning oil. 9

10 Models of the Unit Process and Emissions 5 Gas Reforming unit: Endothermic Reaction favored by high temperature and low pressure. The reaction produces 1:3 CO/H 2 instead of the 1:2 needed for MeOH synthesis, so CO 2 is imported to the unit and in water-gas shift reaction, CO 2 is shifted back to CO by consuming some H 2. The CO 2 to CH 4 molar feeds ratio needs to be 1:3 to get 1:2 CO to H 2 for MeOH synthesis, though any incomplete conversion of CO 2 would call for a slightly higher feeds ratio. Unconverted CO 2 will be purged from the synthesis loop. Methanol unit: The converter in Lurgi LP plant is a cooled multi-tubular reactor. The heat of reaction is directly used to generate high pressure steam F H F H F H MeOH MeOH purge purge j j j CH, H O, CO Q F Q out MeOH MET

11 Models of the Unit Process and Emissions 6 SMR Reactor Condition: CH 4 +H 2 O=CO+3H 2 Endothermic Reaction; therefore, during its operation it will be heated via the combustion of natural gas. T= C Methane Conversion more than 95%[13] MeOH Reactor Condition: T= C P=5 MPa Selectivity more than 99% Different Catalysts CO+2H 2 =CH 3 OH CO 2 +3CH4+2H2O=4CH 3 OH 11

12 Schematic description of PI model k COP BF BOF β Coal Coke Oil Air/O2 Ore Limestone Pellet scrap CHP steam Gas Reformer Methanol Reactor Heat Power Steel Slag Co2 methanol MeOH Plant 12

13 Objective Function F more C m ore pel Cpel mcoal Ccoal ( Euro t steel t h Euro t t h Euro t t h Euro t mcoke Ccoke moil Coil mlime Clime t h Euro t t h Euro t t h Euro t m C V C m C scrap scrap o2 o2 co2 co2 3 3 t h Euro t km n h Euro km n t h Euro t mco 2, strip Cstrip mmeoh CMeOH P Cel Qdh Cheat msteel )/ t h Euro t t h Euro t MW Euro MWh MW Euro MWh t h steel. 44 m 2 ( m X m X m X CO Coal C, coal lime C,lime Oil C, Oil 12 m X m X m X m X V Y 12.. m bio Coke, ext C, coke C, bio ls C, ls MeOH C, MeOH CO 2, strip rg CO2, strip Costs in the objective function ) C ore C pellet C coal C coke,ext C oil C lime C O2 C scrap C el C heat C methanol 80 /t 100 /t 145 /t 300 /t 150 /t 30 /t 50 /km 3 n 100 /t 50 /MWh 10 /MWh 250 /t 13

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29 Conclusion 1 Effect of increasing cost of emission is more significant in comparison of cost of biomass. The effect of first and second stage of integration shows that the price of steel will decrease euro/t and euro/t, respectively which the effect of integration increasing by rising the cost of emission. The optimum operational condition of integrated system does not a significant change according the cost of emission and biomass in case study. Both integrated stages produce less CO 2 than steelmaking without integration. 29

30 Conclusion 2 In order to considering the emissions from fossil fuels in the systems, using biomass decreases around 0.2 t CO2 per t steel emission in steel plant without integration. The first and second stage integration will decrease t CO2 per t steel emission in comparison with steelmaking without integration. Production of methanol has increased by increasing of steel production rate and is estimated to be between tone per hour and tone per hour for the first and second stage integration respectively. 30

31 Conclusion and Future works 1 The study has demonstrated that the optimal recycling degree of top gas varies with the cost structure of emissions, CO 2 stripping and will effect in methanol production. - Lower values of top gas recycling at high stripping cost - Max recycling at high cost of emission - Costs of liquid steel are estimated to be 10 Euro/t steel lower than common case. - Min CO 2 emission is found in Max CO 2 cost For state which the cost of emission and stripping are equal (Cco 2 =C strip =20 /t), in lower production rate the optimal condition is in high values of top gas recycling that shows the balance between decreasing CO 2 emission and methanol production in minimization of steel production cost and in higher production rate the condition change to lower β and increasing in CO 2 emission and methanol production. 31

32 Conclusion and Future works 2 By increasing production rate, estimation of the steel cost in case study- will be decreasing in an integrated plant between % which the lower values will decline by increasing the CO 2 emission cost. The costs of liquid steel are estimated to be /t ls lower than for the case without top gas recycling and methanol plant. The price of liquid steel has increased by of 10 and 13 /t when the cost of CO 2 stripping and emission rise by 20 /t respectively. The results show that with the assumed amount of available top gases could be produced nearly tone per hour methanol in an integrated steelmaking plant with top gas recycling in blast furnace. 32

33 Future Works 33

34 Thank you for your attention! Questions, Comments, Remarks, Advice? 34