**Strategies and their Energy Analysis AnalysisforInSituThermalRemediation**

#### **Tian-Tian Li 1, Yun-Ze Li 1,2,3,\*, Zhuang-Zhuang Zhai 4, En-Hui Li 1 and Tong Li 5**

1 School of Aeronautic Science and Engineering, Beihang University, Beijing 100191, China; litiantian@buaa.edu.cn (T.-T.L.); lienhui@buaa.edu.cn (E.-H.L.)

2 Institute of Engineering Thermophysics, North China University of Water Resources and Electric Power, Henan 450045, China


Received: 8 October 2019; Accepted: 20 October 2019; Published: 22 October 2019

**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<sup>−</sup><sup>1</sup> 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.

**Keywords:** contaminated soil; polluted soil; thermal desorption; thermal remediation; energy analysis and exergy analysis; energy saving
