一、引言

　　1. Introduction

　　在全球“雙碳”戰(zhàn)略加速推進(jìn)與能源結(jié)構(gòu)深度變革的背景下，造紙行業(yè)作為傳統(tǒng)高耗能產(chǎn)業(yè)，正面臨減排壓力與資源化轉(zhuǎn)型的雙重挑戰(zhàn)。沼氣作為制漿廢水厭氧處理的副產(chǎn)物，其熱值潛力與碳中性特征使之成為造紙企業(yè)綠色轉(zhuǎn)型的關(guān)鍵突破口。然而，當(dāng)前行業(yè)普遍存在的沼氣利用率低（不足60%）、能源轉(zhuǎn)化模式粗放等問題，嚴(yán)重制約了其經(jīng)濟(jì)與環(huán)境價(jià)值的釋放。從我自己的實(shí)踐出發(fā)，原來采用的是沼氣摻燒工藝，2023年4月，我們開始調(diào)研，本著“多能互補(bǔ)”系統(tǒng)思維，以沼氣資源利用為核心，深度解構(gòu)沼氣提純、熱電聯(lián)產(chǎn)、生物天然氣制備等技術(shù)的協(xié)同創(chuàng)新路徑。通過對比分析鍋爐摻燒、沼氣發(fā)電、提純制氣三大模式的能效表現(xiàn)與經(jīng)濟(jì)性，結(jié)合太陽紙業(yè)企業(yè)的實(shí)證數(shù)據(jù)，得出結(jié)論：沼氣提純技術(shù)可以通過能源品位升級（甲烷濃度>95%）、碳資產(chǎn)增值（CCER開發(fā)）和多元化消納場景（車用燃?xì)?工業(yè)燃料）構(gòu)建復(fù)合價(jià)值網(wǎng)絡(luò)，實(shí)現(xiàn)非常好的經(jīng)濟(jì)效益。

　　Against the backdrop of accelerated global "dual carbon" strategy and deep transformation of energy structure, the paper industry, as a traditional high energy consuming industry, is facing dual challenges of emission reduction pressure and resource transformation. Biogas, as a byproduct of anaerobic treatment of pulp wastewater, has the potential for calorific value and carbon neutrality, making it a key breakthrough for the green transformation of papermaking enterprises. However, the common problems in the current industry, such as low utilization rate of biogas (less than 60%) and extensive energy conversion mode, seriously restrict the release of its economic and environmental value. Starting from my own practice, we originally used the biogas co firing process. In April 2023, we began to investigate and, based on the "multi energy complementarity" system thinking, with the efficient utilization of biogas resources as the core, deeply deconstructed the collaborative innovation path of technologies such as biogas purification, cogeneration, and biogas production. By comparing and analyzing the energy efficiency performance and economy of the three major modes of boiler co firing, biogas power generation, and purified gas production, combined with empirical data from Sun Paper Industry, it is concluded that biogas purification technology can construct a composite value network through energy grade upgrading (methane concentration>95%), carbon asset appreciation (CCER development), and diversified consumption scenarios (vehicle gas/industrial fuel), achieving the best economic benefits.

　　二、沼氣特性概述2.1沼氣來源--厭氧處理工藝鏈（1）目前造紙廢水處理流程：初沉池→調(diào)節(jié)池→UASB/IC反應(yīng)器→好氧處理，其中UASB反應(yīng)器產(chǎn)氣占比達(dá)70%以上；（2）造紙污泥的協(xié)同處理：造紙污泥（含纖維殘?jiān)┙?jīng)中溫（35-37℃）消化，產(chǎn)氣周期15-20天，VS（揮發(fā)性固體）降解率與產(chǎn)氣量呈正相關(guān)（VS每增加1%，產(chǎn)氣量提升0.5m/t）；（3）原料差異性影響：廢紙制漿沼氣含硫量高（HS>1500ppm），原生漿沼氣硫含量低（HS<800ppm）；非木漿（如竹漿）沼氣甲烷含量較木漿低3-5個百分點(diǎn)。2.2沼氣成分與熱值的動態(tài)分析（1）硫化氫處理必要性：HS濃度>200ppm時，燃?xì)庠O(shè)備腐蝕速率加快3倍（參考《燃?xì)廨啓C(jī)腐蝕控制標(biāo)準(zhǔn)GB/T 14090》）；脫硫成本占比：生物脫硫法0.1-0.2元/m，化學(xué)吸收法0.3-0.5元/m；（2）熱值波動管理：甲烷濃度每下降5%，鍋爐熱效率降低2%；典型熱值應(yīng)用場景：發(fā)電需>22MJ/m，車用燃?xì)庑?gt;31MJ/m（需提純至CH>90%）。2.3體量測算模型（1）產(chǎn)氣量計(jì)算公式：Q =k×COD負(fù)荷×η×R其中： k：產(chǎn)氣系數(shù)（0.35-0.45m/kg COD）     η：COD去除率（85-95%）；     R：運(yùn)行穩(wěn)定性系數(shù)（0.8-0.95）；（2）沼氣利用規(guī)模經(jīng)濟(jì)閾值：提純項(xiàng)目盈虧平衡點(diǎn)：沼氣量≥1500m/d；發(fā)電項(xiàng)目經(jīng)濟(jì)性拐點(diǎn)：設(shè)備利用率>75%（年運(yùn)行6500小時）。

　　2、 Overview of Biogas Characteristics 2.1 Biogas Source - Anaerobic Treatment Process Chain (1) Currently, the papermaking wastewater treatment process includes: primary sedimentation tank → regulating tank → UASB/IC reactor → aerobic treatment, with UASB reactor producing more than 70% of the gas; (2) Collaborative treatment of papermaking sludge: papermaking sludge (including fiber residue) is digested at medium temperature (35-37 ℃), with a gas production cycle of 15-20 days. The degradation rate of volatile solids (VS) is positively correlated with gas production (for every 1% increase in VS, the gas production increases by 0.5m/t); (3) The impact of differences in raw materials: the sulfur content of waste paper pulp biogas is high (HS>1500ppm), while the sulfur content of primary pulp biogas is low (HS<800ppm); The methane content of non wood pulp (such as bamboo pulp) biogas is 3-5 percentage points lower than that of wood pulp. 2.2 Dynamic analysis of biogas composition and calorific value (1) Necessity of hydrogen sulfide treatment: When the HS concentration is greater than 200ppm, the corrosion rate of gas equipment accelerates by three times (refer to the "Gas Turbine Corrosion Control Standard GB/T 14090"); Cost proportion of desulfurization: 0.1-0.2 yuan/m for biological desulfurization method, 0.3-0.5 yuan/m for chemical absorption method; (2) Heat value fluctuation management: for every 5% decrease in methane concentration, the boiler thermal efficiency decreases by 2%; Typical application scenarios for calorific value: power generation requires>22MJ/m, and automotive gas requires>31MJ/m (purified to CH>90%). 2.3 Volume Calculation Model (1) Gas Production Calculation Formula: Q=k × COD Load × η × R, where k: Gas Production Coefficient (0.35-0.45m/kg COD) η: COD Removal Rate (85-95%); R: Operating stability coefficient (0.8-0.95); (2) Scale economy threshold for biogas utilization: breakeven point for purification projects: biogas volume ≥ 1500m/d; Economic turning point of power generation projects: equipment utilization rate>75% (annual operation of 6500 hours).

　　三、沼氣利用模式分析3.1自備熱電廠鍋爐摻燒模式摻燒模式是目前非常普遍的沼氣利用模式，通過污水廠厭氧塔的沼氣穩(wěn)壓罐及后面的風(fēng)機(jī)，通過管道送到電廠的分氣缸，然后通過燃燒器后進(jìn)入鍋爐的燃燒系統(tǒng)。此模式的關(guān)鍵問題點(diǎn)我認(rèn)為有兩處：一是摻燒沼氣雖然投資小、系統(tǒng)簡單，但是其在鍋爐內(nèi)部的摻燒對鍋爐產(chǎn)生氮氧化物有很大影響，通過我實(shí)際的情況來看，一旦投入摻燒系統(tǒng)，脫硝用氨水量馬上增加。如果有兩個沼氣燃燒器運(yùn)行，就相當(dāng)于增加了兩個燃燒源，大大影響鍋爐氮氧化物的產(chǎn)生量。二是沼氣熱值高，但是進(jìn)入爐膛后，實(shí)際產(chǎn)生的熱效率的大小需要試驗(yàn)確認(rèn)，也就是說，其產(chǎn)生的熱效率并不等于鍋爐熱效率。沼氣在燃煤鍋爐內(nèi)燃燒充分，但是到尾部換熱卻不能完全完成。我們組織了試驗(yàn)，沼氣投入鍋爐，穩(wěn)定燃燒后，在尾部煙氣處測量組份，沒有可燃元素，那就說明沼氣的燃盡率是100%；但同時發(fā)現(xiàn)鍋爐的排煙溫度馬上上升，排煙熱損失增加，說明在鍋爐內(nèi)沼氣燃燒熱效率是低于煤炭燃燒熱效率的。下面是實(shí)際的簡單試驗(yàn)的結(jié)果：（1）沼氣輸入熱量：Q1=單位小時沼氣摻燒量*沼氣低位發(fā)熱量=1400m3*24.4mj/m3=81.58萬大卡；（2）排煙熱損失：Q2=12.8萬大卡（3）沼氣燃燒熱效率計(jì)算：η=1-Q/Q1=77.6%在我們這臺特定鍋爐中摻燒，沼氣在鍋爐實(shí)際熱效率為77.6%。如果5000大卡煤炭價(jià)格為800元，那一立方沼氣的經(jīng)濟(jì)價(jià)值是：24.4/4.1868/5000*800*0.77=0.72元。另外，需要提醒的是：“碳減排盲區(qū)”：摻燒模式因無法準(zhǔn)確計(jì)量沼氣替代率，導(dǎo)致CCER（國家核證自愿減排量）開發(fā)難度大。3.2沼氣發(fā)電模式考慮到現(xiàn)在企業(yè)經(jīng)濟(jì)情況不景氣，我們開始的項(xiàng)目原則就定位為“乙方投資，乙方運(yùn)維”的模式，我們把沼氣交于對方，對方提供電力和低壓工業(yè)用蒸汽給我方。

　　3、 Analysis of Biogas Utilization Mode 3.1 Co firing Mode of Self provided Thermal Power Plant Boiler Co firing Mode is currently the most common biogas utilization mode. It is sent through the biogas stabilizing tank of the anaerobic tower in the sewage plant and the fan behind it, through pipelines to the power plant's gas separation cylinder, and then enters the combustion system of the boiler after passing through the burner. I think there are two key issues with this model: firstly, although the investment in co firing biogas is small and the system is simple, its co firing inside the boiler has a significant impact on the production of nitrogen oxides. Based on my actual situation, once the co firing system is put into use, the amount of ammonia water used for denitrification immediately increases. If there are two biogas burners running, it is equivalent to adding two combustion sources, greatly affecting the production of nitrogen oxides in the boiler. The second reason is that biogas has a high calorific value, but the actual thermal efficiency generated after entering the furnace needs to be confirmed through experiments, which means that the thermal efficiency generated does not equal the boiler thermal efficiency. Biogas is fully burned in coal-fired boilers, but the heat exchange at the tail cannot be fully completed. We organized an experiment and put biogas into the boiler. After stable combustion, the composition was measured at the tail flue gas. If there were no combustible elements, it means that the combustion rate of biogas is 100%; But at the same time, it was found that the exhaust temperature of the boiler immediately increased, and the exhaust heat loss increased, indicating that the thermal efficiency of biogas combustion in the boiler is lower than that of coal combustion. The following are the results of a simple experiment: (1) Input heat of biogas: Q1=unit hour biogas co firing amount * biogas low-level heat generation=1400m3 * 24.4mj/m3=815800 kcal; (2) Smoke exhaust heat loss: Q2=128000 kcal (3) Calculation of biogas combustion thermal efficiency: η=1-Q/Q1=77.6%. In our specific boiler, the actual thermal efficiency of biogas in the boiler is 77.6%. If the price of 5000 kcal coal is 800 yuan, the economic value of one cubic meter of biogas is 24.4/4.1868/5000 * 800 * 0.77=0.72 yuan. In addition, it should be noted that there is a "carbon emission reduction blind spot": the co firing mode is difficult to develop due to the inability to accurately measure the biogas substitution rate, making CCER (National Certified Voluntary Emission Reduction) challenging. 3.2 Biogas Power Generation Mode Considering the current economic downturn of the enterprise, our initial project principle is positioned as a "Party B investment, Party B operation and maintenance" model. We hand over the biogas to the other party, who provides us with electricity and low-pressure industrial steam.

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