Optimal design of conformable adsorbed natural gas tanks

Among all applications of natural gas (NG) technologies, natural gas vehicles (NGVs) are one of the primary fields that could take advantage of this cheaper and cleaner energy. Compressed natural gas (CNG) stores NG under high-pressure (20 MPa or 2900~3600 psi) tanks and dominates the current NGVs. With advances in adsorbed natural gas (ANG) storage technology, tank design could be conformal because of low-pressure (3.5 MPa or 500 psi) adsorption by activated carbon pellets. Thus, a conformal tank design can achieve higher space efficiency than traditional cylindrical-shaped tanks. This article focuses on the optimal design of conformal tanks for ANG storage. The objective was to minimize tank mass over the internal volume, considering the shapes of available space. Conformal tank optimization was carried out using the MATLAB optimization program by defining the optimization problem as a mixed-integer nonlinear programming (MINLP) problem. Constraints in the MINLP problem included stress, space efficiency (conformability factor), and dimension. Finite element analysis was employed to verify the stresses. The optimization of the conformable ANG tank design can facilitate home fueling of NGVs since lower internal pressure results in lower tank and compressor costs and lower energy consumption for fueling.