Energy-Saving Strategies and their Energy Analysis and Exergy Analysis for In Situ Thermal Remediation System of Polluted-Soil

Abstract

The environmental safety of soil has become a severe problem in China with the boost of industrialization. Polluted-soil thermal remediation is a kind of suitable remediation technology for large-scale heavily contaminated industrial soil, with the advantages of being usable in off-grid areas and with a high fuel to energy conversion rate. Research on energy-saving strategies is beneficial for resource utilization. Focused on energy saving and efficiency promotion of polluted-soil in situ thermal remediation system, this paper presents three energy-saving strategies: Variable-condition mode (VCM), heat-returning mode (HRM) and air-preheating mode (APM). The energy analysis based on the first law of thermodynamics and exergy analysis based on the second law of thermodynamics are completed. By comparing the results, the most effective part of the energy-saving strategy for variable-condition mode is that high savings in the amount of natural gas (NG) used can be achieved, from 0.1124 to 0.0299 kg·s−1 in the first stage. Energy-saving strategies for heat-returning mode and air-preheating mode have higher utilization ratios than the basic method (BM) for the reason they make full use of waste heat. As a whole, a combination of energy-saving strategies can improve the fuel savings and energy efficiency at the same time.

Planned Heating Control Strategy and Thermodynamic Modeling of a Natural Gas Thermal Desorption System for Contaminated Soil

“…According to Equations (5) and (6), the natural gas mass flow rate Gg and the air mass flow rate Ga can be separately expressed by Equations (29) and (30), correspondingly. Furthermore, the natural gas inlet pressure Pg and the air inlet pressure Pa can be obtained by Equations (31) and (32), where Pb is inlet pressure of the burner. Given the flow resistance of the inlet natural gas pipe R g and that of the inlet air pipe R a calculated from Equation (24), the parallel flow resistance R par [49,50] can be presented by Equation (25), where φ g and φ a characterize the valve opening of the inlet natural gas pipe and air pipe.…”

“…According to Equations (5) and (6), the natural gas mass flow rate G g and the air mass flow rate G a can be separately expressed by Equations (29) and (30), correspondingly. Furthermore, the natural gas inlet pressure P g and the air inlet pressure P a can be obtained by Equations (31) and (32), where P b is inlet pressure of the burner.…”

“…Due to the disadvantages of the aforementioned experimental research, a lumped-parameter method is employed in the present study in order to investigate the influence of moisture migration on the heating performance of the soil. Furthermore, other correlative studies [31][32][33] by our team using a numerical simulation method or a lumped-parameter method have been conducted and published online.…”

Comparison of Three Energy-Saving Strategies Based on Models Established for In Situ Gas Thermal Remediation of Contaminated Soil

“…Among the limited cases, Li et al [2] summarized three energy-saving methods: batch treatment, coupling with in situ chemical oxidation, and installing a heat-tracing extraction pipeline. Li et al [11] presented three energy-saving strategies in ISGTR (variable-condition mode, heat-returning mode, and air-preheating mode) and analysed their energy efficiency based on the concentrated parameter model. Owing to the high complexity of the ISGTR system, it is difficult and uneconomical to study and evaluate energy-saving strategies in practical engineering projects.…”

“…Recycle of energy content in off-gas [2] and utilization of waste heat in flue gas [11] are considered two categories of feasible energy-saving methods for ISGTR. Off-gas containing a large number of combustible pollutants is treated through the off-gas treatment system, which increases the operating cost and wastes the combustion heat of pollutants in the offgas.…”