(431c) Techno-Economic Analysis of a Proposed Hybrid Methanol Synthesis Process

K.M. Bentaher, R.J. Machiela, T.N. Rogers(*)

Michigan Technological University, Department of Chemical Engineering 1400 Townsend Drive, Houghton, MI 49931-1295

(*)Corresponding Author

Abstract

Recent advances in drilling technologies, such as horizontal drilling and hydraulic fracturing, have led to shale gas revolution and considerably boosted U.S. natural gas production. Between 2005 and 2011, U.S. dry gas production increased by about 27 percent. This significant increase in the supply of natural gas has driven down its spot market price by more than 50 percent in the past 7 years. Since methanol is a key domestic transportation fuel, gasoline additive, and intermediate for many other important industrial chemicals, methanol production methods that employ a natural gas feedstock are re-evaluated in this paper to take advantage of the sharp drop in natural gas prices.

In this study, the starting point is the conventional methanol synthesis process which has a recycled syngas stream merging with the methanol synthesis reactorâ??s feed stream. This recycle loop requires a compressor that represents a significant operating expense. To eliminate the syngas recycle loop, a new hybrid process is proposed (Figure 1) that consists of a conventional methanol synthesis reactor (R-1) followed by a reactor (R-2) that condenses methanol vapor as it forms to achieve nearly complete one- pass conversion of syngas to methanol. By condensing methanol vapor on a cooling surface that spirals down the reactorâ??s interior, the equilibrium limitation on methanol conversion is removed. The small amount of syngas that is not converted, rather than being recycled, is used as fuel in the reformer. The upstream conventional methanol synthesis reactor R-1 is included to decrease the R-2 reactorâ??s feed rate, thereby reducing its size and cutting its high capital cost. The novelty of the new hybrid process is in the arrangement of conventional, proven equipment and technologies.

After-tax discounted cash flow analysis is used in this study to incrementally compare the new hybrid process design to two alternative approaches: conventional methanol synthesis with recycle and a process employing a single pass condensing reactor only. Cash flow analysis is also used to establish the optimum ratio of the sizes of reactors R-1 and R-2. Several standard metrics for profitability, such as NPV, ROI, IRR, and payback period, are reported for each candidate process over a 10-year analysis window.

Figure 1. Proposed Hybrid Process for Converting Natural Gas to Methanol