Methanol Technology
Methanol Process Technolog y With some 40 years experience in the methanol business Davy Process Technology is the world’s leading provider of methanol technologies. More than 30 plants using these technologies have been built in 16 countries accounting for more than 40% of the world’s methanol capacity. Davy Process Technology’s reforming experience and its range of synthesis gas technologies are key strengths, as is its wide experience with the core methanol technology from Johnson Matthey Catalysts (previ ously part of ICI). Since 1985 Davy Process Technology has been responsible for the process development of approximately 75% of the plants using this technology. The technology can produce AA grade methanol for chemical applications or alternative grades for olefin production, fuel use or power generation. We have licensed technologies for plants with single stream capacities up to 2.4 million tonnes per year (6700 tonnes per day) using the Davy Process Technology reactor technology in conjunction with Johnson Matthey’s world renowned methanol synthesis catalysts and process technology. Designs have also been developed for larger plants for a range of feedstocks.
M5000 Reform er Tri nidad
The Process Option s We offer a wide range of process technologies that can be applied to methanol production. Synthesis gas can be generated by steam reforming (conventional steam methane reformer or Compact Reformer) or by oxygen reforming (gas heated reforming, combined reforming or auto thermal reforming). Steam or gas cooled reactors are available for methanol synthesis and one, two or three column distillation is used for the production of purified product. The breadth of technology solutions available to us allows us to custom design a flow sheet to reflect any particular project situation, be it large or small, onshore or offshore, for chemical, fuel power generation or MTO use. Reforming Options Steam Methane Reforming Compact Reforming Auto Thermal Reforming (ATR) Combined Reforming Gas Heated Reforming
Feed Gas Clean Up
CRG PreReforming
Methanol Synthesis Options Each and every methanol loop is custom designed to provide the optimal energy and capital solution for a given production capacity and raw gas composition.
Reforming Compression
Gasified Source
Shift/ Sour Shift
Methanol Synthesis Loop
Distillation
Clean Up
Davy Process Technology supplies technology designs for a wide range of feedstock sources (gas, coal, petroleum coke, etc.) and the type of design matches each client’s particular requirements. We custom design every flowsheet from feedstock to product specifications to optimise energy and meet capital constraints. This brochure illustrates a range of features of our methanol technology and we recommend direct contact with our specialists to determine the solution to match specific requirements.
Methanol Synth esis Davy Process Technology together with Johnson Matthey Catalysts is a leading provider of methanol technology which is delivered via world class reactor concepts. Here, we describe some of the features of our designs: Tube Cooled Converter Catalyst
The tube cooled converter is a simple reactor which uses the feed gas to control the temperature in the catalyst bed. Fresh feed gas enters at the bottom of the reactor and is preheated as it flows upwards through tubes in the catalyst bed. The heated feed gas leaves the top of the tubes and flows down through the catalyst bed where the reaction takes place. The heat of reaction is removed by counter-current exchange with feed gas resulting in a temperature profile that approximates to the maximum rate curve. Operated in this manner the reactor achieves good catalyst utilisation. The internals are relatively simple having to be designed only for the differential pressure. Tube thicknesses are kept to a minimum and there are no tube sheet construction problems. With the catalyst on the shell side of the reactor a low cost reactor with an efficient catalyst volume is achieved. As with all axial flow reactors, there is a limit to bed depth due to pressure drop constraints. This together with maximum diameters set by manufacturing or shipping limits means that the maximum capacity possible from a single reactor is about 2,500 TPD. Above this capacity multiple reactors are required.
Feed gas Product gas
Steam and water outlet
Radial Flow Steam Raising Con verter This steam raising converter is a radial flow reactor with catalyst contained on the shell side and steam in the tubes. Fresh feed gas enters at the bottom of the reactor through a central perforated-wall distributor pipe. The gas then flows radially out through the catalyst bed from the inside to out. Water from a steam drum enters at the bottom of the vessel, and flows upwards through the tubes where it is partially vaporised, removing the heat generated by the reaction before returning to the steam drum. The reaction temperature is controlled by varying the steam pressure inside tubes embedded in the catalyst bed. This arrangement gives an excellent temperature profile through the catalyst bed minimising the catalyst required. With a radial flow design the vessel tan to tan height can be increased to maximise the capacity of the reactor without increasing the reactor diameter or the loop pressure drop. Such a concept permits designs for the highest capacity of methanol production in a single reactor to be achieved with capacities up to 3,500 TPD possible. This makes the reactor particularly suited to large capacity plants or for locations where shipping restrictions limit the diameter of the reactor. Ax ial Flo w Cat aly st in Tub es The axial flow catalyst in tube reactor is another form of steam raising converter. As for the radial reactor, the reaction temperature is controlled by varying the steam pressure. This arrangement gives a good temperature profile through the catalyst bed minimising the catalyst required and gives efficient heat recovery to steam. The reactor does however require a thick tube sheets that limits the maximum capacity of the reactor to around 1500 TPD and requires a large number of tubes to accommodate the catalyst. This tends to make this reactor choice a costly one. As part of the development of this type of reactor, Davy Process Technology constructed both mathematical and physical models and the results over a range of conditions were calibrated against real plant tests. Computational Fluid Dynamics (CFD) is the design tool of choice for a radial-flow converter and a quarter-scale model of a segment of the reactor was built so that the CFD results could be compared with water-flow trials. The results were in close comparison and provided criteria to proceed with sizing of plant designs. Davy Process Technology now uses these proven simulation programmes for new plant designs.
Catalyst Product Gas
Product Gas
Inert fill
Water
Water
Synthesis Loo p Configuration Particularly for large plants there is an incentive to increase the conversion in the loop and reduce the loop circulation rate. This is exemplified in a Series Synthesis Arrangement as shown below. Our Methanol Technology incorporates a number of flowsheet improvements which give further benefits of larger single stream capacities, lower capital cost, reduced energy consumption and, longer on-stream periods. The key improvements to the flowsheet can include Catalytic Rich Gas (CRG) prereforming technology combined with the Davy Process Technology Steam Raising Reactor in the methanol synthesis loop. These combined features are considered when the feed gas has a significant CO 2 content to reduce the size of the radiant box, recover more energy thereby increasing efficiency, reduce the size of the steam system, provide more efficient methanol synthesis and to reduce the methanol loop operating pressure Davy Process Technology has no preconceived ideas about the design of large methanol plants. We work with each client to arrive at the optimum solution. We have an entirely original approach to the design of synthesis loops. Particularly for large plants there is an incentive to increase conversion in the loop and reduce circulation rate. We offer three types of converter: Gas/Tube Cooled, Quench and Steam Raising. These may be used singly or in series and combined with any of our reformer techniques. These reactor options are shown below. Steam Raising Loop
Gas/Tube Cooled Loop
Quench Loop
Steam
Syngas
Product
Syngas
Product
Syngas
Product
Any of these loop flowsheets may be combined with any of the reformi ng described elswhere. M oreover it is possible to design combined reformers with series converters with each unit sized to give the whole flowsheet optimum performance. Consequently, there are many permutations of arrangements and every case is judged on client preferred economics in order to develop the best process configuration that will deliver the chosen quality of methanol product to market with maximum profit. A simple Steam Reformer and Gas/Tube Cooled Converter Loop is shown in the flowsheet below. Steam Reforming w ith Tube Cooled Methanol Converter Fuel
BFW
Air Gas Feed
Steam
Innovativ e Large Scale Desig ns
Product
The following example provides an illustration of two approaches to one application. A Gas Heated Reformer was combined with a Gas/Tube Cooled converter with high conversion at a low temperature and a Water Cooled Converter using saturator water as the cooling fluid so that the heat recovered goes back into generating process steam. The second approach is a novel arrangement comprising a radial flow Steam Reformer with an axial Steam Raising Converter. Compared to a conventional large capacity synthesis loop, this design operates with 30% lower recycle while achieving very high conversion and requiring low catalyst volumes. For large scale designs it is appropriate to have two methanol converters in series. A gas heated reformer may be combined with a gas/tube converter followed by a water cooled converter using saturator water as the cooling fluid. The major part of the reaction is carried out in a conventional gas/tube cooled converter, but to get the best possible conversion it is necessary to reach equilibrium at a lower temperature. This is done in a steam raising converter using saturator water as the cooling fluid so that the heat recovered goes back into generating process steam, equivalent to raising steam at 50 bar on a GHR + ATR plant. This arrangement allows methanol content to be as high as 10% with low recycle gas flow rate so that axial flow reactors can continue to be used up to 6,000 TPD or higher. Davy Process Technology has developed a new synthesis loop technology that is also suitable for large scale designs. In this approach, a conventional steam reformer is combined with two identical reactors in series. These may be twin radial fl ow steamraising converters, axial steam-raising converters or gas/tube cooled converters. Compared to a conventional methanol synthesis loop, this new design operates with an approximately 30% lower recycle ratio while achieving very high conversion with low catalyst volumes.
Distillation Davy Process Technology offers a range of designs of methanol distillation systems. Depending on the destined market and appropriate specification, two or three column flowsheets may be chosen. The figure below shows the three column system used for the recent M5000 plant in Trinidad.
The 5000 MTPD plant flowsheet designed by Davy Process Technology and operated in Trinidad uses a single topping column but the larger refining columns are split into two because a single 5000 MTPD column is too big to ship to most sites around the world. The design of internals including trays and gas and liquid distributors is achieved using detailed hydraulic modelling in order to ensure that accurate flow distribution is maintained under changing process conditions. When we look to the future, it is likely that methanol will continue to be an internationally traded commodity chemical and also have outlets as a fuel component and a captive intermediate. Consequently, not all methanol plants will be making AA-grade methanol and for a lower specification product, a totally single-stream 5000 MTPD distillation train becomes feasible and further advantages of the economics of scale become realisable.
Reforming and Gas Feed Treatment Davy Process Technology in conjunction with Johnson Matthey Catalysts provides processes to utilise a wide range of hydrocarbon sources in methanol synthesis. We have designs for extensive ranges of methane rich gases that may include carbon dioxide, nitrogen and heavier hydrocarbons. We also provide designs for gases generated from coal, shale oil, refinery petrocoke and sub-surface coal gasification. We treat, condition or purify these gases so they are suitable for one of our extensive range of reforming technologies, including: -
Steam Reforming Compact Reforming Auto Thermal Reforming Combined Reforming Gas Heated Reforming
We also work closely with different gasification technologies and have, with Johnson Matthey Catalysts, flowsheet designs and catalysts to process and condition gases that need shift, impurity removal and CO 2 removal. We illustrate our expertise in the following associated Carbon Conversion Technologies brochures:
Gas Conditioni ng and Purification Synthesis Gas Technology Compact Reformer & GTL Technologies
Synthesis Gas Compression The Davy Process Technology flowsheet incorporates a turbine in the second stage of the synthesis gas compressor. Even with a turbine limit (for high-speed duty) of 70MW further improvements have been made to enable the flowsheet to deliver in excess of 6500 MPTD of methanol. These include permutations of the following options: • • •
reduction of the discharge (loop) pressure housing the circulator in a separate casing adding carbon oxides
Reducing the loop pressure is more than counterbalanced by improvements in synthesis reactor design and reduced rate of circulation from enhanced catalyst performance with higher specific conversion efficiency.
Reliabilit y and Cost Eff ectiveness Davy Process Technology’s tried and tested steam reforming route to methanol will continue to be used for many applications provided the limits of design and performance continue to be extended. In this way, new plants inherit reliability gained over many design cycles but have single stream capacity of double the limit that seemed possible only ten years ago. Designs for such large plants use equipment normally employed in the utility industries such as power generating stations. As piping and valves become larger, wall thickness increases and weight rises so that they need their own support structures. Each scale-up development demands extension of specifications in terms of materials of construction, fabrication tolerances and novel systems for installation and increasing the scale of operation imposes tighter limits on reliability and ease of maintenance. Davy Process Technology ensures that all these requirements are managed within projects that in scale and value are major infrastructure contracts. The new designs of very large methanol plants are so reliable that they increase plant availability and as cost effectiveness is directly related to plant availability this is the motivation to improve process technology. Further economic improvements will derive from integrating reforming, methanol synthesis and conversion to olefins. These developments must be coupled with detailed design of all the component parts so that proven reliability is built in. Davy Process Technology has the reputation for supplying the most commercially attractive methanol process technology and is actively working to extend both size range and process flexibility. We are determined to stay in the vanguard of these developments and will continue to work with the major plant operators to deliver the most cost effective process solutions.
Products The predominant chemical used for methanol is as the raw material for acetic acid and formaldehyde production, an important component in the manufacture of urea formaldehyde resins for the construction industry. It is also used as a solvent, a fuel and in power generation. It is also seen as a future intermediate in the production of olefins (MTO). Technologies are also available for the conversion of methanol to dimethyl ether (DME) which can be used as a fuel either in a gas turbine or a power station.
Methanol Production Offshor e Davy Process Technology is working with a group of clients who are interested in taking methanol technology offshore to access new gas sources. For such cl ients we can offer a variety of solutions: All the major technical and safety issues have been addressed and satisfactory solutions have been found for catalyst loading/unloading in a ship environment. Equipment optimisation has been completed with innovative integration into a commercial flow sheet capable of producing 2,500 tonnes/day of methanol. If a project has gas and offshore operation is an option, then the first consideration is the type of structure. There are two basic types that are appropriate: a fixed system such as a CGS (Concrete Gravity Structure) and an FPSO (Floating Production, Storage and Offloading). Fixed Platform A CGS becomes in effect an artificial island. The structure can be constructed in a yard and then floated to the location where it is to be sited. This can be done with the process equipment in place which enables construction to take place in a low construction cost location. Once at the production location the GCS is ballasted to sink it into place. This type of structure therefore requires relatively shallow water near to the gas well head. An example of a project that is following this approach is the Methanol Australia project that is planned to be located on the Tassie Shoal. For this type of structure the topside weight is not a major issue as it is supported from the sea bed. There is also no limit to the plot space available and therefore no particular limit to the size of plant that can be built on this type of structure. Additional plot is expensive and so technologies that minimise plot space are still desirable. On the CGS, the process unit will be deck mounted with the utilities below deck and the storage of methanol within the CGS. As the GCS is fixed to the sea bed, vessel motion is not an is sue and therefore any of the synthesis gas technologies presented above could be used on this type of structure. Floating Production A FPSO is in effect a boat with all that is necessary to produce the oil, gas and methanol contained on it. The vessel will have a mooring system to hold it in place, gas processing, methanol production, utilities, product storage and accommodation for the crew and operators. The process plant and utilities will be installed on the topside with storage below deck. This vessel is readily movable and therefore is suited to use on fields with limited lives. In addition MFPSOs can beneficial where there is perceived country risk and the operator wants to have the ability to move its plant assets to alternative locations. The MFPSO is a boat and therefore space and weight are substantially more important than for a CGS. In addition the vessel will be subject to motion and this needs to be carefully considered when selecting the process technology. In general it is expected that the MFPSO option will have a higher cost than the CGS and therefore if the water depth and field life is sufficiently long we would expect a fixed platform to be the first choice. Vessel motion, weight and space are the key considerations for MFPSO plants. Most methanol plants involve the use of a steam reformer be it in a conventional or combined reforming process. Steam reformers are large and heavy items and the refractory systems and unrestrained tube systems mean that they are not suitable for the movement that can be experienced on a FPSO. The very large fired heater necessary for autothermal reforming is also not suited to such movement. This leaves two technologies that can be adapted for use on a FPSO: Compact Reforming and Gas Heated Reforming. These technologies also have the benefit of saving both space and weight. As mentioned earlier the compact reformer can accommodate gas with high levels of CO2 without the need for CO2 removal and is therefore particularly suited to processing of high CO2 gas on a FPSO. Floating Distillation An operator who is c onsidering an offshore project will also have to consider if the project should refine the methanol on the FPSO. If the methanol is to be used only for MTO applications it may not be necessary to perform any distillation. If the entire production is going to pass through a single terminal, the methanol could be refined at the terminal before being distributed to customers. These options would reduce the size and weight of the topsides required, however it would require the additional weight of the water in the crude to be shipped in the product. This may add to the shipping weight depending on the production technology used. The operator may wish to be able to transport material directly from the FPSO to their customers and in this case offshore refining will be needed.
