An approach to grading coalbed methane resources in China for the purpose of implementing a differential production subsidy

The heterogeneity of coalbed methane(CBM) resources was not taken into account when the current indiscriminate subsidy policy was developed. In it, limited subsidy funds are given first to high-quality resources and even to subsidize profitable projects. Thus, the policy has had less than the intended effect in improving CBM production. To implement a new type of differential subsidy, it is necessary to grade the CBM resources, as will be discussed in this paper. After the factors affecting the resources value are systemically examined, sorted and merged, the relationship between the key factors and economic value is analyzed by an engineering economics method, and the production profile type, peak production(or stable production) and buried depth are used as grading factors. The production profile type is used to categorize, and peak production and buried depth are used to grade resources within the same category. The grading method is as follows: use subsidy levels at the economic critical point(NPV = 0) to identify the grades of resources, and determine the combination of peak production and buried depth for different resources grades base on indifference curves drawn according to the relationship between the economic value and peak production and buried depth.

The importance of coil conductivity and eddy current effects in the analysis of electromagnetic forming process

Coil design and performance analysis are critical for the electromagnetic forming(EMF)process.However,previous studies have paid little attention to the coil con-ductivity,and the influence of eddy current effects in coil conductors on the forming process has not been well understood.This work aims to address these problems through numerical and experimental investigations.It is found that,due to the eddy current effects,the uneven current distribution appears in the coil conductors that should be considered when analysing the forming process,especially for the cases with large heights of coil conductors.Meanwhile,an important and interesting discovery is that the eddy current effects can greatly reduce the sensitivity of the coil conductivity with respect to the workpiece deformation,the Joule heating and the temperature rise in the coil.For instance,compared to a forming system with a copper coil,the forming height of the workpiece in the forming system with an AA5083‐O coil is reduced by less than 5%under the same discharge energy,while the copper conductivity is 3.3 times that of the latter.These results are helpful to understand the EMF process and achieve the optimal design of coils.