国外修复案例丨原位热脱附技术处理PCBs污染土

案例摘要

Site Name: Former Mare Island Naval Shipyard/场地名称

Location:California/所在位置

Period of Operation /项目执行时间

September to December 1997/9-12月

Cleanup Authority/清理机构

California EPA

Purpose/Significance of Application/目的与意义

Field demonstration of in situ thermal desorption to treat PCBs in shallow  and deep contaminated soils/采用原位热脱附技术处理浅层与深层PCBs污染土。

Cleanup Type: Field demonstration/清理类型：现场示范

Contaminants: PCBs/主要污染物

• PCB levels were measured as high as 2,200 mg/kg, with an average of 220  mg/kg during a RI/污染物最高浓度与平均浓度(RI所指应为remedial  investigation，修复性调查，或可等同于国内的第二阶段场地调查;在资料中也常连用为RI/FS，FS应为feasibility  study，可行性研究，或可等同于国内的技术方案编制)

Waste Source: Contaminated wash water disged to  soil/废弃物来源：排放到土壤中的(变压器)洗涤污染水

Technology/技术

In-Situ Thermal Desorption (ISTD)/原位热脱附

Two demonstrations were conducted a thermal well and a thermal blanket -using  the MU-125 (125 cfm capacity) unit/主要采用热处理井与热处理毯两种工艺

12 thermal/vapor extraction wells, installed to a depth of 14 ft bgs and  screened from 6 inches to 14 ft, used to treat deeper  soil/共12口热处理/气相抽提井处理较深层污染土

Two thermal blankets used to treat shallow soils/共两套热处理毯处理浅层污染土

Emissions control system included a flameless thermal oxidation unit, a heat  exchanger, and GAC augmented with pelletized calcium  hydroxide/尾气控制系统组成：一套无焰热氧化单元，一台换热器和采用氢氧化钙造粒的颗粒活性炭单元。

Heating was conducted for a total of 35 days (over a period of 3 months) to  reach the target temperature of 600°F at four central monitoring  locations/在3个月的时间内，累计进行了35天的热量传导，以便将四个中央监控位置加热到600°F(约315℃)的目标温度。(本段因无更多参考资料，根据时间判断和语义分析，判断可能是分时段加热，请专家指正)

Process flow rates ranged from 38 to 82 scfm/工艺流量变化范围

Type/Quantity of Media Treated/受污染介质类型及水文地质条件

Soil

Aquifer material - siltstone/fine-grained sandstone/含水层：粉砂岩/细砂岩

Groundwater depth - approximately 9 feet to 15 feet bgs/地下水埋深(BGS应为below  ground surface/地面下，折合约2.7-4.6米)

Moisture content - approximately 20%/含水量

Porosity - approximately 30%/孔隙率

Regulatory Requirements/Cleanup Goals/清理要求及目标

The primary performance objective for the demonstration was to treat PCBs in  soil to a concentration of less than 2 mg/kg/最初设定的修复目标值

Off-gas limits included an HCL emission rate limit of 4.0 lbs/hr/尾气排放限值

Results/清理成效

All post-treatment samples had total PCB concentrations below the  quantitation limit (10 μg/kg) and met the performance objective of<2  mg/kg/所有处理后的样本总PCB浓度均低于其定量限界，满足修复目标要求。

On average, the thermal wells reduced total PCBs from 53,540 μg/kg to<10  μg/kg, to a 12 ft depth/平均而言，热处理井将12英尺范围内的PCBs浓度降到了10以下。

On average, the thermal blankets reduced total PCBs from 20,607 μg/kg to<10 μg/kg, to a 1 ft depth/平均而言，热处理毯将1英尺范围内的PCBs浓度降低至了10以下。

The HCl emission rate limit of 4.0 lbs/hr was not exceeded during the  demonstration/在实施期间HCL排放率未超过限值。

CO emissions were below 10 ppmV with a mean concentration of approximately 2  ppmV/CO排放浓度低于10，平均为2。

Total hydrocarbon emissions ranged from 0 to 8 ppmV with a median disge  rate of less than 0.002 lb/hr as CH4/总碳氢化合物排放范围0-8，其中CH4低于0.002。

Excess oxygen was 12%, except during the change over to the thermal  blanket/除热处理毯切换期间外，余氧率为12%，

Costs/费用

Actual construction and operating costs for this project are not  available/本项目无实际施工费用和运行费用(据后文，应仅为TEST SITE/试验场地)

Depending on site-specific factors, the vendor has established an overall  cost range of approximately $100 to $250 per  ton/依据现场实际情况，供应商的处理单价为$100~250/吨(1997)。

Description/案例综述

The Former Mare Island Naval Shipyard includes an electrical workshop, known  as Building 866, which was used from 1955 to 1994. From 1955 to 1978,  transformers washed in the workshop contained polychlorinated biphenyl (PCB)  oils, which were drained and washed into a 30-gallon sump through floor grates  and drains. The liquid waste and sludge that accumulated in the sump were pumped  to a 3,000 gallon grease trap near the western corner of the building.

The test site was located in the area of the former grease trap and adjacent  paved areas located at the northwest corner of Building 866.

Levels of PCBs as high as 2,200 mg/kg were identified at the site during the  remedial investigation. A demonstration of In-Situ Thermal Desorption (ISTD)  usingthermal blankets and thermal wells was conducted in this area by the U.S.  Navy and the Bay Area Defense Conversion Action Team (BADCAT) Environmental  Technology Project (ETP).

ISTD is a combination of thermal desorption and vacuum extraction, and is  conducted in-situ. Two demonstrations were conducted (thermal well and thermal  blanket) and were found to be effective in treating PCB impacted soils,  achieving the performance objective of 2 mg/kg. The results of the  demonstrations suggested minor modifications in well heater materials, control,  and monitoring to aid in more even soil heating and extend heater life and  efficiency. The heater

failures experienced on this project were attributable to the use of 316  stainless steel heater strips (rather than 310 stainless steel), and the  initially high operating temperature of  heaters./请注意本项目的失败之处是，采用了316材质的不锈钢条加热器(而不是310);加热器初始温度过高。(正文完)