一、引言

　　1. Introduction

　　在全球“雙碳”戰(zhàn)略加速推進與能源結構深度變革的背景下，造紙行業(yè)作為傳統(tǒng)高耗能產業(yè)，正面臨減排壓力與資源化轉型的雙重挑戰(zhàn)。沼氣作為制漿廢水厭氧處理的副產物，其熱值潛力與碳中性特征使之成為造紙企業(yè)綠色轉型的關鍵突破口。然而，當前行業(yè)普遍存在的沼氣利用率低（不足60%）、能源轉化模式粗放等問題，嚴重制約了其經濟與環(huán)境價值的釋放。從我自己的實踐出發(fā)，原來采用的是沼氣摻燒工藝，2023年4月，我們開始調研，本著“多能互補”系統(tǒng)思維，以沼氣資源高效利用為核心，深度解構沼氣提純、熱電聯(lián)產、生物天然氣制備等技術的協(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)與經濟性，結合太陽紙業(yè)企業(yè)的實證數(shù)據，得出結論：沼氣提純技術可以通過能源品位升級（甲烷濃度>95%）、碳資產增值（CCER開發(fā)）和多元化消納場景（車用燃氣/工業(yè)燃料）構建復合價值網絡，實現(xiàn)最好的經濟效益。

　　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、 Overview of Biogas Characteristics

　　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→調節(jié)池→UASB/IC反應器→好氧處理，其中UASB反應器產氣占比達70%以上；

　　2.1 Source of Biogas - 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;

　?。?）造紙污泥的協(xié)同處理：造紙污泥（含纖維殘渣）經中溫（35-37℃）消化，產氣周期15-20天，VS（揮發(fā)性固體）降解率與產氣量呈正相關（VS每增加1%，產氣量提升0.5m/t）；

　　(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);

　?。?）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。2.2沼氣成分與熱值的動態(tài)分析

　　(3) The impact of differences in raw materials: the sulfur content of waste paper pulp biogas is high (H-S>1500ppm), while the sulfur content of primary pulp biogas is low (H-S<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）硫化氫處理必要性：HS濃度>200ppm時，燃氣設備腐蝕速率加快3倍（參考《燃氣輪機腐蝕控制標準GB/T 14090》）；脫硫成本占比：生物脫硫法0.1-0.2元/m，化學吸收法0.3-0.5元/m；

　　(1) The necessity of hydrogen sulfide treatment: When the concentration of H2S 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;

　?。?）熱值波動管理：甲烷濃度每下降5%，鍋爐熱效率降低2%；典型熱值應用場景：發(fā)電需>22MJ/m，車用燃氣需>31MJ/m（需提純至CH>90%）。2.3體量測算模型（1）產氣量計算公式：Q =k×COD負荷×η×R其中： 

　　(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 Does car gas require>31MJ/m (To be purified to CH>90%). 2.3 Volume Calculation Model (1) Gas Production Calculation Formula: Q=k × COD Load × η × R Where:

　　k：產氣系數(shù)（0.35-0.45m/kg COD）    

　　k: Gas production coefficient (0.35-0.45m/kg COD)      

　　η：COD去除率（85-95%）；    

　　η: COD removal rate (85-95%);      

　　R：運行穩(wěn)定性系數(shù)（0.8-0.95）；

　　R: Operating stability coefficient (0.8-0.95);

　?。?）沼氣利用規(guī)模經濟閾值：提純項目盈虧平衡點：沼氣量≥1500m/d；發(fā)電項目經濟性拐點：設備利用率>75%（年運行6500小時）。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最普遍的沼氣利用模式，通過污水廠厭氧塔的沼氣穩(wěn)壓罐及后面的風機，通過管道送到電廠的分氣缸，然后通過燃燒器后進入鍋爐的燃燒系統(tǒng)。此模式的關鍵問題點我認為有兩處：一是摻燒沼氣雖然投資小、系統(tǒng)簡單，但是其在鍋爐內部的摻燒對鍋爐產生氮氧化物有很大影響，通過我實際的情況來看，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行，就相當于增加了兩個燃燒源，大大影響鍋爐氮氧化物的產生量。

　　(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). 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.

　　二是沼氣熱值高，但是進入爐膛后，實際產生的熱效率的大小需要試驗確認，也就是說，其產生的熱效率并不等于鍋爐熱效率。沼氣在燃煤鍋爐內燃燒充分，但是到尾部換熱卻不能完全完成。我們組織了試驗，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，說明在鍋爐內沼氣燃燒熱效率是低于煤炭燃燒熱效率的。下面是實際的簡單試驗的結果：

　　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. Here are the actual results of a simple experiment:

　?。?）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；

　　(1) Biogas input heat: Q1=unit hour biogas co firing amount * biogas low-level heat generation=1400m3 * 24.4mj/m3=815800 kcal;

　　（2）排煙熱損失：Q2=12.8萬大卡

　　(2) Smoke exhaust heat loss: Q2=128000 kcal

　?。?）沼氣燃燒熱效率計算：η=1-Q/Q1=77.6%在我們這臺特定鍋爐中摻燒，沼氣在鍋爐實際熱效率為77.6%。如果5000大卡煤炭價格為800元，那一立方沼氣的經濟價值是：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)”：摻燒模式因無法精確計量沼氣替代率，導致CCER（國家核證自愿減排量）開發(fā)難度大。

　　(3) Calculation of thermal efficiency of biogas combustion: η=1-Q/Q1=77.6%. In our specific boiler, when co fired, 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沼氣發(fā)電模式考慮到現(xiàn)在企業(yè)經濟情況不景氣，我們開始的項目原則就定位為“乙方投資，乙方運維”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。具體配置及經濟性核算如下：沼氣低熱值MJ24.4日供應沼氣量m/d100000機組配置功率Mw13.80發(fā)電量Kw13310機組供電量Kw12645年運行小時數(shù)h8000機組每小時蒸汽量t/h7.50供電供汽年度總收益萬元/年3739.單位沼氣價值元1.123.3沼氣提純模式沼氣提純制生物天然氣（Bio-CNG）模式，是通過膜分離、PSA（變壓吸附）或水洗工藝將沼氣甲烷濃度提純至90%~97%，生產車用燃氣或工業(yè)燃料。此模式附加值最高（生物天然氣售價達3.5~4.5元/m），且可開發(fā)碳信用（CCER收益15~30元/噸CO）。下表是目前各提純工藝的優(yōu)劣勢的對比分析表：工藝名稱甲烷得率能耗適用規(guī)模核心優(yōu)勢主要局限變壓吸附90%~95%0.25~0.35>1000m/d自動化高，純度穩(wěn)定吸附劑更換成本高膜分離80%~88%0.15~0.25200~2000m/d低能耗，模塊化靈活膜污染風險，預處理嚴格水洗法85%~90%0.3~0.5500~3000m/d脫碳徹底，工藝簡單水耗大，廢水處理難化學吸收（胺法）>99%0.4~0.6>1500m/d高純度，同步脫硫溶劑損耗，環(huán)保壓力深冷分離>99.5%0.8~1.2>5000m/d生產LNG，附加值極高投資與能耗雙高能耗單位：（kWh/m）

　　3.2 Considering the current economic downturn of the enterprise, our initial project principle was positioned as a "Party B investment, Party B operation and maintenance" model. We handed over the biogas to the other party, who provided us with electricity and low-pressure industrial steam. The specific configuration and economic calculation are as follows: the low calorific value of biogas MJ24.4, the daily supply of biogas m/d100000, the unit configuration power Mw13.80, the power generation Kw13310, the unit power supply Kw12645, the operating hours h8000, the hourly steam volume t/h7.50, the annual total revenue of power supply steam is RMB 3739. The unit biogas value is RMB 1.123.3. The biogas purification mode is to purify biogas to produce bio natural gas (Bio CNG), which purifies the methane concentration of biogas to 90%~97% through membrane separation, PSA (pressure swing adsorption) or water washing process, and produces vehicle gas or industrial fuel. This mode has the highest added value (the selling price of biogas reaches 3.5-4.5 yuan/m), and can also develop carbon credits (CCER income of 15-30 yuan/ton CO). The following table is a comparative analysis of the advantages and disadvantages of various purification processes at present: process name, methane yield, energy consumption, applicable scale, core advantages mainly limited to pressure swing adsorption 90%~95%, 0.25~0.35>1000m/d, high automation, stable purity, high adsorbent replacement cost, membrane separation 80%~88%, 0.15~0.25, 200~2000m/d, low energy consumption, modular flexible membrane pollution risk, strict pre-treatment, water washing method 85%~90%, 0.3~0.5500~3000m/d, complete decarbonization, simple process, high water consumption, difficult chemical absorption of wastewater treatment (amine method)>99%, 0.4~0.6>1500m/d, high purity, synchronous desulfurization solvent loss, environmental pressure cryogenic separation>99.5%, 0.8~1.2>5000m/d for LNG production, added value. High investment and energy consumption double high energy consumption unit: (kWh/m)

　　四、結論

　　4、 Conclusion

　　通過現(xiàn)場調研，我們去了杭州臨港的現(xiàn)場考察，拿到第一手資料，所以經過綜合論證，決定采用“沼氣提純”的模式來進行沼氣資源的高效利用。從經濟性角度看，每立方的沼氣產生的價值為：摻燒模式0.72元，沼氣發(fā)電模式約為1.12元，而沼氣提純模式，在目前能源條件下，由乙方負責投資和運維的情況下，每方沼氣的價值將大于前面兩種模式。所以，我們選擇了沼氣提純模式來運作此項目，也是企業(yè)能源工作在“多能互補”方面做出的一大有益嘗試。目前，太陽紙業(yè)是國內唯一明確披露沼氣提純生產生物天然氣的造紙企業(yè)，其項目覆蓋國內外多個基地，技術成熟且效益顯著。根據2019年數(shù)據，其山東基地的一、二期項目采用EPC模式建設，沼氣處理能力為2×30,000立方米/日，提純后的生物天然氣產量可達2×20,000立方米/日以上。截至2019年，山東基地已累計生產生物天然氣1,385萬立方米，直接并入廠區(qū)市政燃氣管網，用于自用燃料，顯著降低對外部天然氣的依賴。以上，即關于造紙企業(yè)沼氣的高效利用項目的實踐總結，希望對相關企業(yè)的能源管理及項目決策起到一定的參考與借鑒作用。

　　Through on-site research, we went to Hangzhou Lingang for on-site investigation and obtained first-hand information. Therefore, after comprehensive evaluation, we have decided to adopt the "biogas purification" mode for efficient utilization of biogas resources. From an economic perspective, the value generated per cubic meter of biogas is: 0.72 yuan for co firing mode, about 1.12 yuan for biogas power generation mode, and the value per cubic meter of biogas purification mode will be greater than the previous two modes under current energy conditions, with Party B responsible for investment and operation. So, we chose the biogas purification mode to operate this project, which is also a beneficial attempt made by the enterprise's energy work in the aspect of "multi energy complementarity". At present, Sun Paper is the only paper-making enterprise in China that has explicitly disclosed the production of biogas through biogas purification. Its projects cover multiple bases both domestically and internationally, with mature technology and significant benefits. According to 2019 data, the first and second phases of its Shandong base project will be constructed using EPC mode, with a biogas processing capacity of 2 × 30000 cubic meters per day and a purified biogas production of over 2 × 20000 cubic meters per day. As of 2019, the Shandong base has produced a total of 13.85 million cubic meters of bio natural gas, which has been directly integrated into the municipal gas pipeline network in the factory area for self use as fuel, significantly reducing dependence on external natural gas. The above is a practical summary of the efficient utilization project of biogas in papermaking enterprises, hoping to provide some reference and guidance for energy management and project decision-making of related enterprises.