馬 咸 吳建會(huì) 張?jiān)７?孫英明 梁丹妮 馮銀廠

(南開(kāi)大學(xué)環(huán)境科學(xué)與工程學(xué)院，國(guó)家環(huán)境保護(hù)城市空氣顆粒物污染防治重點(diǎn)實(shí)驗(yàn)室，天津 300071)

循環(huán)流化床鍋爐(CFB)廣泛應(yīng)用于發(fā)電、供暖和工業(yè)生產(chǎn)中[1]，是大氣顆粒物的重要排放源。近年來(lái)，大量CFB加裝了脫硫裝置以控制SO2的排放[2]。然而，脫硫裝置在降低顆粒物和SO2排放的同時(shí)，會(huì)改變顆粒物構(gòu)成和模態(tài)分布，進(jìn)而影響其消光作用[3-5]。顆粒物中的硫酸鹽和硝酸鹽等水溶性物質(zhì)是使可見(jiàn)光散射的主要成分[6]。但國(guó)內(nèi)外對(duì)煙氣中顆粒物的水溶性離子特征特別是模態(tài)分布研究仍相當(dāng)有限。本研究利用靜電低壓撞擊器(ELPI+)采集CFB中煙氣的顆粒物樣品，并分析其水溶性離子組成及模態(tài)粒徑分布。

1研究方法

1.1 樣品采樣與分析

選擇3臺(tái)CFB(分別為CFB(a)、CFB(b)、CFB(c))進(jìn)行煙氣中的顆粒物樣品采集。3臺(tái)CFB均采用非選擇催化還原(SNCR)脫硝技術(shù)，未安裝除霧器，其他基本情況見(jiàn)表1。CFB(a)和CFB(c)燃煤摻雜20%(質(zhì)量分?jǐn)?shù)，下同)石灰石，CFB(b)燃煤摻雜20%～30%污泥。

利用顆粒物采樣系統(tǒng)在每臺(tái)CFB的煙道中采集煙氣中粒徑為0.006～10.000 μm的顆粒物樣品，其中粒徑為0.006～0.040 μm的顆粒物未檢出。圖1為顆粒物采樣系統(tǒng)示意圖。根據(jù)3012H型煙氣分析儀測(cè)得的煙氣流速、煙氣溫度等參數(shù)選取等速采樣頭[7-8]。ELPI+可裝載不同粒徑段的鋁膜或Teflon膜采集顆粒物樣品。煙氣經(jīng)過(guò)旋風(fēng)除塵后進(jìn)入稀釋通道，利用經(jīng)過(guò)過(guò)濾、加熱的潔凈空氣按煙氣與空氣體積比為1∶8稀釋煙氣。稀釋通道可在一定程度上反映污染源排放的真實(shí)情況[9]。加熱器對(duì)稀釋通道和旋風(fēng)除塵管路進(jìn)行加熱，以避免煙氣溫度在管路中迅速下降而使煙氣中的水蒸氣凝結(jié)，從而影響顆粒物樣品的采集。單次采樣時(shí)間為6～8 h，每次采集不同粒徑段的膜樣品，共計(jì)84組樣品。顆粒物濃度均使用基準(zhǔn)含氧量6%(體積分?jǐn)?shù))進(jìn)行轉(zhuǎn)化[10]。測(cè)得的標(biāo)準(zhǔn)化質(zhì)量濃度(c’，mg/m3)通過(guò)式(1)可轉(zhuǎn)換得到顆粒物質(zhì)量濃度。

表1 CFB基本情況

注：1)均為質(zhì)量分?jǐn)?shù)。

c’=dc/d(lgD)

(1)

式中：c為顆粒物質(zhì)量濃度，mg/m3；D為顆粒物粒徑，μm。

圖1 顆粒物采樣系統(tǒng)示意圖Fig.1 The sampling system for particulate matter

1.2 質(zhì)量控制

采樣前Teflon膜和鋁膜均進(jìn)行60 ℃恒溫干燥2 h，以去除表面的有機(jī)雜質(zhì)和水分。采樣膜稱量前均置于恒溫((20.0±2.0) ℃)、恒濕(50%±5%)的室內(nèi)平衡72 h至恒量。

2 結(jié)果與討論

2.1 煙氣中不同粒徑顆粒物的濃度分布

3臺(tái)CFB煙道出口顆粒物標(biāo)準(zhǔn)化質(zhì)量濃度粒徑分布譜如圖2所示。PM10、PM2.5和PM1可通過(guò)圖2積分得到。由于CFB(a)和CFB(c)的除塵方式和脫硫方式相同，因此這兩臺(tái)CFB的顆粒物濃度粒徑分布譜基本相似。CFB(a)和CFB(c)的PM10質(zhì)量濃度分別為29.71、23.40 mg/m3，PM2.5質(zhì)量濃度分別為4.32、1.78 mg/m3，PM1質(zhì)量濃度分別為0.05、0.04 mg/m3。CFB(b)的PM10、PM2.5和PM1質(zhì)量濃度分別為3.38、2.17、0.68 mg/m3。CFB(a)和CFB(c)的PM2.5質(zhì)量濃度分別占各自PM10的14.54%、7.61%，CFB(b)的PM2.5質(zhì)量濃度占PM10的64.20%。這可能是由于CFB(b)的袋式除塵器比靜電除塵器對(duì)大粒徑顆粒物有更高的除塵效率[12-13]。

圖2 顆粒物標(biāo)準(zhǔn)化質(zhì)量濃度粒徑分布譜Fig.2 Size distribution of particulate matter standard mass concentration

Table 2 Mass percentage of water-soluble ions in particulate matter %

2.2 顆粒物中的水溶性離子分析

顆粒物中水溶性離子的質(zhì)量分?jǐn)?shù)如表2所示。3臺(tái)CFB的PM10中水溶性總離子質(zhì)量分?jǐn)?shù)基本相同。CFB(b)的PM2.5中水溶性總離子質(zhì)量分?jǐn)?shù)為60.07%，較CFB(a)和CFB(c)中分別高2.86、3.67百分點(diǎn)。CFB(b)的PM1中水溶性總離子質(zhì)量分?jǐn)?shù)為61.33%，與SIPPULA等[14]2974-2982的研究結(jié)果相近，高于CFB(a)和CFB(c)，可能是由于煙氣經(jīng)雙堿濕法技術(shù)脫硫裝置后煙氣溫度較低、濕度較高，易凝結(jié)成超細(xì)顆粒物[15-18]。

圖3 CFB(a)中水溶性離子的模態(tài)粒徑分布Fig.3 Mode distribution of water-soluble ions in CFB(a)

圖4 CFB(b)中水溶性離子的模態(tài)粒徑分布Fig.4 Mode distribution of water-soluble ions in CFB(b)

圖5 CFB(c)中水溶性離子的模態(tài)粒徑分布Fig.5 Mode distribution of water-soluble ions in CFB(c)

3 結(jié) 論

(1) CFB(a)、CFB(b)、CFB(c)的PM10質(zhì)量濃度分別為29.71、3.38、23.40 mg/m3，PM2.5質(zhì)量濃度分別為4.32、2.17、1.78 mg/m3，PM1質(zhì)量濃度分別為0.05、0.68、0.04 mg/m3。

(2) 3臺(tái)CFB的PM10中水溶性總離子質(zhì)量分?jǐn)?shù)基本相同。CFB(b)的PM2.5和PM1中水溶性總離子質(zhì)量分?jǐn)?shù)高于CFB(a)和CFB(c)。

(4) 3臺(tái)CFB的顆粒物中水溶性離子大都呈現(xiàn)雙模態(tài)粒徑分布，包括超細(xì)粒子模態(tài)和粗粒子模態(tài)。

[1] 程樂(lè)鳴,周星龍,鄭成航,等.大型循環(huán)流化床鍋爐的發(fā)展[J].動(dòng)力工程學(xué)報(bào),2008,28(6):817-826.

[2] SCHREIFELS J J,FU Yale,WILSON E J.Sulfur dioxide control in China:policy evolution during the 10th and 11th Five-year Plans and lessons for the future[J].Energy Policy,2012,48(3):779-789.

[3] MEIJ R,WINKEL B.The emissions and environmental impact of PM10and trace elements from a modern coal-fired power plant equipped with ESP and wet FGD[J].Fuel Processing Technology,2004,85(6/7):641-656.

[4] WU Xuecheng,ZHAO Huafeng,ZHANG Yongxin,et al.Measurement of slurry droplets in coal-fired flue gas after WFGD[J].Environmental Geochemistry and Health,2015,37(5):1-15.

[5] COSTELLO M J,JOHNSEN S,GILLILAND K O,et al.Predicted light scattering from particles observed in human age-related nuclear cataracts using mie scattering theory[J].Investigative Ophthalmology & Visual Science,2007,48(1):303-312.

[6] IGNATIUS N T.Chemical and size effects of hygroscopic aerosols on light scattering coefficients[J].Journal of Geophysical Research：Atmospheres,1996,1011(D14):19245-19250.

[7] HILLAMO R E,KAUPPINEN E I.On the performance of the Berner low pressure impactor[J].Aerosol Science and Technology,1991,14(1):33-47.

[8] MARJAMAKI M.Performance evaluation of the Electrical Low-Pressure Impactor (ELPI)[J].Journal of Aerosol Science,2000,31(2):249-261.

[9] HILDEMANN L M,CASS G R,MARKOWSKI G R.A dilution stack sampler for collection of organic aerosol emissions:design,characterization and field tests[J].Aerosol Science and Technology,1989,10(1):193-204.

[10] LATVA SOMPPI J,MOISIO M,KAUPPINEN E I,et al.Ash formation during fluidized-bed incineration of paper mill waste sludge[J].Journal of Aerosol Science,1998,29(4):461-480.

[11] SVENNINGSSON B,RISSLER J,SWIETLICKI E,et al.Hygroscopic growth and critical supersaturations for mixed aerosol particles of inorganic and organic compounds of atmospheric relevance[J].Atmospheric Chemistry & Physics,2005,6(7):1937-1952.

[12] YI Honghong,HAO Jiming,DUAN Lei,et al.Fine particle and trace element emissions from an anthracite coal-fired power plant equipped with a bag-house in China[J].Fuel,2008,87(10/11):2050-2057.

[13] YI Honghong,HAO Jiming,DUAN Lei,et al.Characteristics of inhalable particulate matter concentration and size distribution from power plants in China[J].Journal of the Air & Waste Management Association,2006,56(9):1243-1251.

[14] SIPPULA O,HOKKINEN J,PUUSTINEN H,et al.Particle emissions from small wood-fired district heating units[J].Energy & Fuels,2009,23(6).

[15] 王勇,徐曉虎.燃煤電廠除塵器對(duì)微細(xì)粉塵捕集效率對(duì)比試驗(yàn)[J].中國(guó)環(huán)保產(chǎn)業(yè),2013(6):45-48.

[16] KANG S G,KERSTEIN A R,HELBLE J J,et al.Simulation of residual ash formation during pulverized coal combustion: bimodal ash particle size distribution[J].Aerosol Science and Technology,1990,13(4):401-412.

[17] BUHRE B,HINKLEY J,GUPTA R,et al.Submicron ash formation from coal combustion[J].Fuel,2005,84(10):1206-1214.

[18] 于敦喜,徐明厚,易帆,等.燃煤過(guò)程中顆粒物的形成機(jī)理研究進(jìn)展[J].煤炭轉(zhuǎn)化,2004,27(4):7-12.

[19] 胡月琪,馬召輝,馮亞君,等.北京市燃煤鍋爐煙氣中水溶性離子排放特征[J].環(huán)境科學(xué),2015,36(6):1966-1974.

[20] 郭興明,郝吉明,段雷,等.大容量燃煤電站鍋爐水溶性離子排放特征[J].清華大學(xué)學(xué)報(bào)(自然科學(xué)版),2006,46(12):1991-1994.

[21] 靳曉潔.石灰石—石膏濕法脫硫吸收塔中氯離子問(wèn)題的探討[J].電力科技與環(huán)保,2013,29(1):46-47.

[22] JONES J M,DARVELL L I,BRIDGEMAN T G,et al.An investigation of the thermal and catalytic behaviour of potassium in biomass combustion[J].Proceedings of the Combustion Institute,2007,31(2):1955-1963.

參考文獻(xiàn):

[23] TISSARI J,SIPPULA O,KOUKI J,et al.Fine particle and gas emissions from the combustion of agricultural fuels fired in a 20 kW burner[J].Energy & Fuels,2008,22(3):2033-2042.

[24] SAROFIM A F,HOWARD J B,PADIA A S.The physical transformation of the mineral matter in pulverized coal under simulated combustion conditions[J].Combustion Science and Technology,1977,16(3/4/5/6):187-204.

[25] MCELROY M W,CARR R C,ENSOR D S,et al.Size distribution of fine particles from coal combustion[J].Science,1982,215(4528):13-19.

[26] MATHIEU Y,TZANIS L,SOULARD M,et al.Adsorption of SOxby oxide materials:a review[J].Fuel Processing Technology,2013,114(3):81-100.

[27] 吳忠標(biāo),劉越,譚天恩.雙堿法煙氣脫硫工藝的研究[J].環(huán)境科學(xué)學(xué)報(bào),2001,21(5):534-537.