低碳生產造林規格材之研究

Abstract

本研究依據生命週期評估（Life cycle assessment,LCA）架構評估規格材生產過程中資源投入與產出，使用材積10.73 m3杉木（Cunninghamia lanceolata）原木，生產2 × 6與2 × 4等兩項規格材，尺寸依序為0.14 × 0.038 × 3.6 m3與0.09 × 0.038 × 3.6 m3，生產數量各為116與124支，總材積為3.77 m3，及三項絕乾木質剩餘資材：邊皮材202.34 kg/m3、木粉42.52 kg/m3與鉋屑92.94 kg/m3，最終材積利用率為35.12%，因採用隨機選取部分原木含有腐朽幹空，原木徑級與材積利用率並無直接關係；規格材與木質剩餘資材重量百分比分別為31.56與68.44%wt，三項木質剩餘資材絕乾重與重量百分比為：邊皮材1127.04 kg（34.83%wt）、木粉236.72 kg（7.31%wt）與鉋屑412.45 kg（26.30%wt）。 生產每立方公尺規格材須投入電力、柴油與用於乾燥階段鍋爐燃料-邊皮材，各為77.79 kWh/m3、21.45 L/m3與79.10 kg/m3，其中燃燒邊皮材為碳中和不列入碳排放計算，生產每立方公尺規格材會產生碳排放117.54 kgCO2e/m3，電力消耗與碳排放皆高於國內外研究，除生產規模與製程差異外，與原木形質、製品尺寸，及乾燥階段能源使用化石燃料或再生能源相關。 木顆粒生產過程皆不添加膠合劑，總生產電力消耗分別為木粉255.19 kWh/t、邊皮材203.92 kWh/t與鉋屑399.12kWh/t，三者生產速率偏低導致能源消耗高，尤其鉋屑因片狀、質輕易飄動不利造粒，操作時間長；三項木顆粒直徑皆為D08長度12.25 ~ 29.74 mm，邊皮材木顆粒為三者中最長；含水率皆小於10%；堆積密度分別為邊皮材686 kg/m3、木粉732 kg/m3與鉋屑784 kg/m3，熱值個別為18.73、18.75與18.76 MJ/kg；木顆粒灰份含量高到低:邊皮材(0.31%)>木粉(0.11%)>鉋屑(0.04%)；三項木顆粒因機械堅牢度不足，皆無法用做產業用途木顆粒，作為商業與住宅用途僅有鉋屑木顆粒符合標準等級B。

This paper uses Life cycle assessment (LCA) to calculate inputs and outputs of China fir (Cunninghamia lanceolate) primary timber products production process. A total of 10.73 m3 of China fir logs were used to produce two primary timber products: 2 × 6 (0.14 × 0.038 × 3.6 m3) and 2 × 4 (0.09 × 0.038 × 3.6 m3).The unmbers of 2 × 6 and 2 × 4 primary timber products of fir respectively are 116 and 124 (total utilizable volume of primary timber products is 3.77 m3, the final volume utilization rate is 35.12%) and three types of absolute dry weight wood residuals: Slab wood (202.34 kg/m3), Saw dust (42.52 kg/m3) and Four side planer shaving (92.94 kg/m3). Some China fir logs are decayed and hollow trunk, so there is no direct relationship between log diameter grade and volume utilization rate. The weight percentages of primary timber products and wood residuals are 31.56 and 68.44%wt respectively. The dry weight and weight percentages of the three types of wood residuals: Slab wood 1127.04 kg (34.83%wt), Saw dust 236.72 kg (7.31%wt) and Four side planer shaving 412.45 kg (26.30%wt). The production of each cubic meter of primary timber products require electricity (77.79 kWh/m3), diesel (21.45 L/m3)and boiler fuel for drying stage - slab wood (79.10 kg/m3) and emit 117.54 kgCO2e/m3.The combustion of slab wood is considered carbon neutral and is not included in carbon emissions calculations.Electricity consumption and carbon emissions are both higher than previous researches.Production scale, process mode, properties of wood log, product size and categories of energy sources will all affect carbon emissions. No adhesive is added wood pellets in this study, and the total production electricity consumption is 255.19 kWh/t for saw dust, 203.92 kWh/t for slab wood, and 399.12 kWh/t for four side planer shaving. Low wood pellet production rate leads to high energy consumption. In particular, the shape and weight of four side planer shaving require longer operating times during the pellet production stage.The diameter of the three type of wood pellets is classified as D08 and the length ranges from 12.25 ~ 29.74 mm.The moisture content of the three types of wood pellets are less than 10%.The bulk densities of wood pellets: Slab wood (686 kg/m3), Saw dust (732 kg/m3) and Four side planer shaving (784 kg/m3), and the calorific values are 18.73, 18.75 and 18.76 MJ/kg respectively. The bark contains a high ash content. The ash content of wood pellets ranges from high to low: Slab wood (0.31%) > Saw dust Saw dust (0.11%) > Four side planer shaving (0.04%).Three types of wood pellets cannot be used for industrial purposes due to insufficient mechanical durability. Only four side planer shaving pellets comply with standard class B for commercial and residential use.