煤制甲醇工艺9.docx

1、煤制甲醇工艺9AIChE 2008 National Student Design CompetitionCoal to Methanol Chemical Plant ReportChi Hang LeeMan Kit ChanChan Yau AoUniversity of California, San DiegoDepartment of Mechanical and Aerospace EngineeringChemical Engineering Program9th June, 2008Professor Pao ChauContentsExecutive Summary .1O

2、verall Project Scope Description .1Design Basis, Principle and Limitations .2Technology Selection Criteria and Conclusion.5Process Performance Summary .9Project Economics Summary .17Project Description .18Process Flow Diagram .19Major Equipment and List .21Environmental and Process Safety .21Appendi

3、x A: Coal Input Calculations Appendix B: Higman Gasification Simulation OutputAppendix C: Water Gas Shift Reaction CalculationsAppendix D: Methanol Synthesis Rate CalculationsAppendix E: Temperature vs. CO2 and H2S with NMPAppendix F: NMP Cost CalculationAppendix G: ASPEN Input FileAppendix H: ASPEN

4、 Simulation Appendix I: Equipment Sizing Calculation1. Goal Gasifier 2. Acid Gas Removal Tower3. Water Gas Shift Reactor4. Flash Drum 5. Distillation Tower 16. Distillation Tower 2Appendix J: Economic Analysis for PFRAppendix K: CAPCOST ModelAppendix L: Overall Process Flow DiagramExecutive Summary

5、As the price of crude oil continues to increase, there is a raising need to produce an alternate fuel source Methanol is an attractive contest and in this project, the economic feasibility and a preliminary design for a chemical plant to produce methanol to coal is explored. Design will be completed

6、 with the computer model ASPEN, while the economic is carried out utilizing CAPCOST. The desired output of methanol is 5000 MT/day and must also meet the AA grade requirement. This preliminary design is capable of producing 5065 MT/day of methanol, the plant is designed based on 292 days per year an

7、d 24 hours operation schedule. The internal rate of return on investment is 0.13% and a paid back period of 19.3 year. Overall Project Scope DescriptionThis study serves to provide a preliminary design for a coal-to-methanol process and to determine the economic feasibility of the project. Location

8、of the plant has been decided to be on the US Texas Gulf Coast, and a capacity to produce 5000 MT per day of methanol is desired. Methanol produced must meet the AA methanol grade purity specification. The process will start by selecting a coal source out of three types of coal. It is assumed that t

9、he selected coal has been pre-processed at an estimated cost and transferred into a gasifier in which coal is reacted with steam and oxygen producing a syngas containing unreacted steam, H2, N2, CH4, H2S, CO2, CO and NH3. The syngas will then be subjected to a separation unit for acid gas removal. T

10、he H2S concentration in the treated syngas will be reduced to less than 0.1 ppmv before entering the water gas shift reactor. In the water gas shift reactor, the stoichiometric ratio between H2 and CO in the clean syngas is shifted to the desired ratio of 2:1. This specific ratio is needed to favor

11、the production yield of methanol in the methanol synthesis process which consists of a series of five adiabatic plug flow reactors with inter-stage cooling systems. The methanol produced will then be refined in order to meet the specific AA grade requirement. The overall process of the design is pre

12、sented in Fig.1 below.Fig. 1. Block flow diagram of coal-to-methanol process. Methanol produced can be sold at a price of $320/MT (US Gulf Coast FOB). An economic analysis of the coal-to-methanol process will also be performed to evaluate the economic feasibility of the plant. Key numbers such as ca

13、pital cost, operating cost, project internal rate of return (IRR), sensitivity of the project economic and payback period will all be considered when determining the overall economic feasibility. Besides, the environmental and safety of the methanol production plant will also be analyzed and conside

14、red when evaluating the environmental feasibility of the design. Design Basis, Principles and LimitationsCoal GasificationVarious calculations in this design are performed using MT/day as the basis. In the coal gasification process, the governing chemical reactions can be generalized as the followin

15、g reaction:CxHy + x/2 O2 xCO + y/2 H2 (1)Since the gasifier operates at high temperature (in excess of 1500 C)and pressure (3200 kPa), it can be modeled as equilibrium reactors assuming near-complete carbon conversion using the following set of reactions: CO + H2O CO2 + H2 (2)C + CO2 2 CO (3)C + H2O

16、 CO + H2 (4)These reactions are assumed to at thermodynamic equilibrium and are used as a basis to determine the relative concentrations in the syngas generated from the gasifier. Acid Gas RemovalThe syngas produced from the gasifier is treated by an acid gas removal process. There are many commerci

17、al acid gas technologies in the industry and one of the technologies will be used as a basis of the design. The chosen acid gas removal technology should have a high selectivity for H2S relative to CO2 and be able reduce the sulfur level of the treated syngas to 0.1 ppmv or lower. In this design pro

18、ject, the acid gas removal process is approximated as a simple separation unit to achieve the specified sulfur level of the treated syngas. The removal of CO2 during this process will also be considered to in order to account for the carbon loss during the coal-to-methanol process. Water Gas Shift R

19、eactor The basic chemistry in the water gas shift reactor can be represented as the following reaction:CO + H2O CO2 + H2 (5)The purpose of the water gas shift reaction is to adjust the ratio of H2 to CO to 2:1. The temperature of the water gas shift reactor ranges from 600-900 F (315.6-482.2 C) and

20、the pressure is approximately at 500 lb/in2 (3447 kPa). The equilibrium constant at different temperatures can be calculated using the equation below: (Eq.1)Based on the calculated equilibrium constant, the amount of steam feeding to the water gas shift reactor can be determined.Methanol Synthesis D

21、uring the methanol synthesis process, three chemical reactions have to be considered:CO + 2H2 CH3OH (6)CO2 + H2 CO + H2O (7)CO2 + 3H2 CH3OH + H2O (8)2CO + 4H2 C2H5OH + H2O (9)These reactions are simultaneous reactions in the methanol synthesis reactors. Reaction (5) is the water gas shift reaction,

22、reaction (8) is the methanol synthesis from carbon dioxide, reaction (9) is the production of byproduct (ethanol) and reaction (6) is considered to be the basic reaction for the synthesis of methanol because CO is the most effective component for production of methanol and reaction (6) is the rate d

23、etermining step. The expression of equilibrium constant for reaction (6) with temperature range (373 673 K) is: (Eq.2) The kinetics of the reactions above can be found from the literature. Based on the kinetics of those reactions, the production yield of each chemical component in the syngas can be

24、calculated. The kinetic rate expressions for each reaction are presented as follows: (Eq.3) (Eq.4) (Eq.5)These are the kinetic rate expressions for reaction (6), (7) and (8). The value of the parameters are described and given in Appendix. The kinetic rate of reaction (9) is assumed to be 100 times

25、slower than the production rate of methanol, so the kinetic rate expression for ethanol synthesis will be equation (6) divided by 100. Adiabatic quenched bed reactors with Cu-Zn-Al catalysts are used for methanol synthesis. Considering the kinetic rate expressions and reactions above, the production

26、 yield of methanol can be found from Aspen simulation. The methanol production rate is required to be slightly greater than 5000 MT/day prior to the methanol refining process. Such methanol production rate can be achieved by varying the amount of catalysts and the number of reactors. Methanol Refine

27、ry The design of the methanol refining process must be able to achieve AA methanol grade purity specification. The final product should contain greater than 99.85 % w/w methanol (dry basis), less than 0.1% w/w water and less than 50 ppmw ethanol. More than one distillator may be required to meet the

28、 purity specification.Technology Selection Criteria and ConclusionCoal Selection The design of the coal-to-methanol process begins with coal selection and pre-processing. Three coal sources were being considered, which are Martin Lake Texas Lignite, Montana Sub- Bituminous and Illinois Bituminous. M

29、ontana Sub-Bituminous was chosen to be the coal source based upon the characteristics of the three coals provided. Montana coal contains high carbon content and the least moisture and sulfur contents among the three coals. The gasification of high carbon content coal can generate more carbon-contain

30、ing synthesis gas such as carbon monoxide and carbon dioxide, and thus can lead to a better yield of methanol in the methanol synthesis process. The low sulfur content in coal creates less acid gas, and thus leads to a lower waste treatment cost in the removal of sulfur in the acid gas removal stage

31、. Table 1. Coal Sources and CompositionGasification Technology Selection There are three choices of gasification technologies which are moving-bed, fluid-bed and entrained-flow gasification processes. The choice of gasification process has been decided to employ the use of entrained-flow single stage gasifier because this process gives a higher carbon conversion to CO than the other two processes. The low CO2 and high carbon conversion ensures that almost all carbon in the feed is converted to CO, and hence a non-s