(756b) Thermo-Economic Optimization of a Novel Zero Carbon Emission Polygeneration Plant Based On Methane Oxidative Coupling of Shale Gas and Nickel-Oxide Combustion Processes

Thermo-economic
optimization of a novel zero carbon emission polygeneration plant based on
methane oxidative coupling of shale gas and nickel-oxide combustion processes

Yaser
Khojasteh Salkuyeh, Thomas A. Adams II

Department of Chemical Engineering, McMaster
University, 1280 Main St W, Hamilton, Ontario, L8S 4L7, Canada.

Despite serious challenges on
crude oil supply and price, the demand for petrochemical products is growing
fast. This concern provides an incentive for petrochemical complexes to find
new resources as feedstock, such as new approaches for production of olefins
(petrochemical feeds) from natural gas. On the other side, the increasing
natural gas supply due to remarkable growth in shale gas reservoirs in
developed countries has made some significant shocks in the difference between
the natural gas and oil prices. This drop in gas price indicates that new
adaptations for the worldwide energy supply chains are required. In this work,
a novel process for ethylene and ethane production is developed by integrating an
oxidative coupling of methane (OCM) process for olefin production with a Nickel-oxide
(NiO) chemical looping combustion (CLC) power generation process with zero carbon
emissions. A simplified process diagram of this system is shown in figure 1. The
aim of this system is to increase the adoptability of natural gas-based
processes by connecting them to petrochemical complexes. The major limitations
of OCM process are its low olefin yield and selectivity with high product
separation difficulty, which lead to a significant ratio of unreacted gas.
Therefore, the strategy of this polygeneration plant is to recover and use this
unreacted gas efficiently. The CLC approach is investigated for electricity generation
using portions of the unreacted gas. It is a promising alternative for electricity
generation without any greenhouse gas emission that uses NiO as oxygen carrier.
NiO is reduced to Ni by combusting the inlet gas in the reducer reactor, and
then regenerated in the oxidizer with fresh air to complete the cycle [1].
The fully heat-integrated process is modeled in the Aspen Plus simulation
program.

Fig.
1. Co-production of power, ethylene and ethane with 100% carbon capture

The OCM reactor is a catalytic
(La₂O₃/CaO) reactor that operates isothermally at about
800°C and atmospheric pressure and converts methane to ethylene. The reactor
simulation utilizes a reduced model derived from experimentally observed data provided
by Godini et al. [2]
as a function of the inlet CH₄ to oxygen ratio. This ratio, along
with the recycle ratio of unreacted gas from the product recovery section, are the
two major decision variables that affect the thermal efficiency and net present
value (NPV) of the plant. Diglycol-Amine (DGA) is used for CO₂
removal of outlet gas. Its energy requirement is less than previous work that
used MDEA [2].
In addition, a detailed model for gas turbine is built to calculate the cooling
requirement of blade surfaces. This model is a significant improvement over the
classic turbine models in Aspen Plus because the details of how the cooling
management system is implemented can significantly impact the actual performance
of the power generation section. This model was developed in Visual Basic and connected
to Aspen Plus via the Microsoft Excel interface. Furthermore, economic
evaluation is performed by using Aspen Icarus Process Evaluator for direct
capital cost and updated values of economic parameters for 2000 tonne/day natural
gas and 30 years lifetime.

An integrable particle swarm
optimization (PSO) model [3]
is established in Matlab for the thermo-economic optimization of process. The highest
obtainable thermal efficiency is about 40.9% LHV (37.5% HHV) with 3.97 for the
optimal ratio of inlet shale gas to oxygen, and no recycle of unreacted gas to
the OCM reactor. However, from an economical point of view, about 30.6%
improvement on NPV and 24% reduction on thermal efficiency will be achieved compared
to thermal optimum point, when the objective function is switched to NPV. The
optimal recycle ratio is changed to the maximum allowable ratio in this case
with NG/O₂=3.75. In addition, a sensitivity analysis on optimum
ratio is performed to define the match point of the operating conditions of
both scenarios. The final results show that they match when ethylene and ethane
prices are about 40% of their base case values. This means
the price of liquid products are currently high enough to sacrifice thermal
efficiency in order to achieve a higher NPV.

References

[1]
B. Moghtaderi, Review of the Recent Chemical Looping Process Developments for
Novel Energy and Fuel Applications, Energy & Fuels, 26 (2011) 15-40.

[2] H.R. Godini,
S. Xiao, S. Jašo, S. Stünkel, D. Salerno, N.X. Son, S. Song, G. Wozny,
Techno-economic analysis of integrating the methane oxidative coupling and
methane reforming processes, Fuel Processing Technology, (2012).

[3] D. Sedighizadeh, E. Masehian, Particle swarm
optimization methods, taxonomy and applications, International Journal of
Computer Theory and Engineering, 1 (2009) 1793-8201.