1 Gasification coupling power generation process

生物質耦合發電主要有3種方式，直接耦合、氣化耦合和蒸汽耦合。直接耦合是研磨過的生物質與燃煤直接在電廠鍋爐中混燃的工藝過程；氣化耦合則需要設置單獨氣化爐，生物質氣化后將產出的燃氣引入電廠鍋爐中混燃；生物質在單獨設置的鍋爐中燃燒，產出的蒸汽并入電廠鍋爐蒸汽聯箱的工藝則被稱為蒸汽耦合。

There are three main ways of biomass coupling power generation: direct coupling, gasification coupling and steam coupling. Direct coupling refers to the process of mixing pulverized biomass and coal directly in the boiler of power plant; For gasification coupling, a separate gasifier needs to be set. After biomass gasification, the produced gas will be introduced into the boiler of the power plant for mixed combustion; The process that biomass is burned in a separately set boiler and the generated steam is incorporated into the steam header of the power plant boiler is called steam coupling.

不同耦合方式工藝特點各異，基于耦合發電技術成熟的歐洲地區的應用情況，對不同耦合方式發電效率及單位投資進行了對比，對比結果如表1所示。

The process characteristics of different coupling modes are different. Based on the application of the mature coupling power generation technology in Europe, the power generation efficiency and unit investment of different coupling modes are compared. The comparison results are shown in Table 1.

從對比數據來看，直接耦合的方式在改造費用及發電效率方面均處于優勢地位，但對生物質種類及預處理深度要求較高，容易產生結渣及腐蝕問題，同時也會影響燃煤鍋爐的灰渣性質，降低利用價值。蒸汽耦合通過單獨設置燃燒鍋爐避免了生物質對原有設備的影響，生物質混燃比例僅收到發電汽機制約，但是需要單獨增設除塵等凈化系統，投資成本將大大增加。氣化耦合發電效率與蒸汽耦合接近，但投資成本減少了近1/2，通過氣化方式減少了生物質對燃煤鍋爐的影響，擴大了可消納原料的種類，便于灰分的收集及綜合利用，同時可以利用現有的空氣凈化系統達到排放要求，是比較理想的耦合方式。因此，考慮到耦合發電計量問題及國家政策的傾斜，生物質氣化將成為主流的耦合工藝。

From the comparison data, the direct coupling method is in an advantageous position in terms of transformation cost and power generation efficiency, but it has high requirements on biomass type and pretreatment depth, which is easy to cause slagging and corrosion problems, and will also affect the ash properties of coal-fired boilers and reduce the utilization value. The steam coupling avoids the impact of biomass on the original equipment by setting a combustion boiler separately. The proportion of biomass mixed combustion is only limited by the power generation steam turbine, but it needs to add a separate purification system such as dust removal, which will greatly increase the investment cost. The efficiency of gasification coupling power generation is close to that of steam coupling, but the investment cost has been reduced by nearly 1/2. Through gasification, the impact of biomass on coal-fired boilers has been reduced, the types of consumable raw materials have been expanded, which is convenient for the collection and comprehensive utilization of ash, and the existing air purification system can be used to meet the emission requirements, which is an ideal coupling method. Therefore, biomass gasification will become the mainstream coupling process in consideration of the coupling power generation metering problem and the inclination of national policies.

2生物質氣化爐技術比較

2 Comparison of biomass gasifier technologies

生物質氣化反應需要在氣化爐內完成，根據氣固接觸方式的不同，生物質氣化爐主要分為固定床（上吸式、下吸式）、流化床（鼓泡流化床、循環流化床）和氣流床；根據運行壓力不同可分為常壓、加壓氣化爐。氣流床對生物質粒徑要求較高（顆粒＜3mm），并不適用于大規模的生物質處理過程，因此，現行的生物質氣化技術一般是固定床及流化床2種類型。固定床及流化床氣化爐結構的差異影響了其處理規模，燃氣特性及品質，從而決定了不同爐型的應用場合。

The biomass gasification reaction needs to be completed in the gasifier. According to the different gas-solid contact modes, the biomass gasifier is mainly divided into fixed bed (upper suction type, lower suction type), fluidized bed (bubbling fluidized bed, circulating fluidized bed) and entrained flow bed; It can be divided into atmospheric and pressurized gasifiers according to different operating pressures. The entrained flow bed has a high requirement on the particle size of biomass (particles<3mm) and is not suitable for large-scale biomass treatment process. Therefore, the current biomass gasification technology is generally fixed bed and fluidized bed. The difference between the structure of fixed bed gasifier and fluidized bed gasifier affects its treatment scale, gas characteristics and quality, thus determining the application occasions of different types of gasifiers.

（1）不同氣化爐型適用規模。固定床氣化爐內部混合程度及熱傳導都比較差，導致難以達到同一截面物料分布、溫度分布、燃氣組成均勻一致，隨著尺寸放大，上述問題將更加嚴重。相對而言，流化床氣化爐雖然對原料的尺寸要求更加嚴格，但其物料及溫度均勻性更好，運行較為穩定，在處理規模上更具優勢。在正常操作條件下，以常規秸稈為原料的不同氣化爐處理能力如圖1所示。由圖1可知，常壓流化床氣化爐的處理能力可達100MW左右（約600t/d），而固定床氣化爐的處理能力不超過10MW（約60t/d）。由于耦合發電需要達到一定規模才具有較高的經濟效益，因此，具有更大處理能力的流化床氣化爐將更具優勢[3]。

(1) Applicable scale of different gasifier types. The mixing degree and heat conduction in the fixed bed gasifier are relatively poor, which makes it difficult to achieve uniform material distribution, temperature distribution and gas composition in the same section. The above problems will become more serious with the size enlargement. Relatively speaking, the fluidized bed gasifier has more strict requirements on the size of raw materials, but its material and temperature uniformity is better, its operation is more stable, and it has more advantages in the treatment scale. Under normal operating conditions, the processing capacity of different gasifiers using conventional straw as raw material is shown in Figure 1. It can be seen from Figure 1 that the processing capacity of the atmospheric fluidized bed gasifier can reach about 100MW (about 600t/d), while the processing capacity of the fixed-bed gasifier does not exceed 10MW (about 60t/d). Since the coupled power generation needs to reach a certain scale to have higher economic benefits, the fluidized bed gasifier with greater processing capacity will have more advantages [3].

（2）不同氣化爐型焦油產量。生物質氣化往往伴隨著焦油的產生，造成能源浪費的同時還降低了氣化效率，還影響了氣化設備的穩定運轉，不經凈化的生物質燃氣還會對后續管路及燃燒設備造成嚴重危害。

(2) Tar output of different gasifiers. Biomass gasification is often accompanied by tar production, which causes energy waste, reduces gasification efficiency, and affects the stable operation of gasification equipment. Unpurified biomass gas will also cause serious harm to subsequent pipelines and combustion equipment.

不同氣化爐由于結構不同，其焦油產生量有比較大的差別，其中上吸式固定床氣化燃氣由于經過低溫區域而無法完全裂解，焦油含量高；下吸式固定床氣化燃氣則可以保證充分的熱解溫度，焦油含量少，鼓泡式及循環流化床氣化爐介于以上2者之間，具體數據見表2[4，6]。

Due to the different structures of different gasifiers, the tar production is quite different, among which the gas from the updraft fixed-bed gasifier cannot be completely cracked because it passes through the low temperature zone, and the tar content is the highest; The downdraft fixed-bed gasification gas can ensure sufficient pyrolysis temperature, with the minimum tar content, and the bubbling and circulating fluidized bed gasifiers are between the above two. See Table 2 [4, 6] for specific data.

（3）不同氣化爐型燃氣成分。生物質燃氣成分是決定燃氣熱值及燃燒性能的關鍵因素，理想的燃氣組分可以保證更高的耦合發電參數。在氣化劑選用空氣的條件下，不同類型氣化爐產出燃氣組成如表3所示。

(3) Gas composition of different gasifier types. The composition of biomass gas is the key factor to determine the calorific value and combustion performance of the gas. The ideal gas composition can ensure higher coupling power generation parameters. Under the condition that air is selected as gasifier, the composition of gas produced by different types of gasifiers is shown in Table 3.

可以看出，固定床與流化床氣化爐燃氣熱值相差不大都具有較高的氣化效率，但由于流化床內部溫度、物料分布更均勻，產氣量、燃氣成分相對穩定，其燃氣的品質更高[4，6]。

It can be seen that the fixed bed gasifier and the fluidized bed gasifier have relatively high gasification efficiency due to the difference in gas calorific value, but because the temperature and material distribution inside the fluidized bed are more uniform, the gas production and gas composition are relatively stable, and the gas quality is higher [4, 6].

（4）氣化耦合發電爐型選擇。固定床氣化爐由于其自身的種種局限性，不適于用于燃煤電廠生物質耦合發電項目。，固定床氣化爐規模較小（一般＜10MW），無法產生規模效應，限制了項目盈利的可能。其次，固定床氣化爐下料過程易產生搭橋現象而控制困難，因此燃氣品質波動較大，影響了鍋爐的安全運行。處理規模相對較大的上吸式固定床因出口燃氣溫度較低（約450℃左右）且波動較大，燃氣內焦油含量高，在輸送過程中存在堵塞管道的風險，也不適用于耦合發電過程。固定床氣化爐更加適用于生物質處理規模較小的情況，其中上吸式固定床比較適用于粗燃氣不需冷卻及凈化的場合，比如直接作為小型鍋爐或加熱爐的燃料或向系統提供工藝熱源；下吸式氣化爐由于產出焦油含量較低，可以較好的和內燃機聯合工作，適用于1MW以下的分布式氣化發電。

(4) Selection of gasification coupling power generation furnace type. Due to its own limitations, fixed bed gasifiers are not suitable for biomass coupling power generation projects in coal-fired power plants. First of all, the fixed bed gasifier has a small scale (generally<10MW) and cannot produce scale effect, which limits the possibility of project profit. Secondly, the feeding process of fixed bed gasifier is easy to produce bridging phenomenon and difficult to control, so the gas quality fluctuates greatly, affecting the safe operation of the boiler. The up-suction fixed bed with relatively large treatment scale is not suitable for the coupled power generation process because of its low outlet gas temperature (about 450 ℃) and large fluctuation, and high tar content in the gas. The fixed-bed gasifier is more suitable for the small scale of biomass treatment, in which the up-suction fixed-bed is more suitable for the occasions where the crude gas does not need to be cooled and purified, such as directly serving as fuel for small boilers or heating furnaces or providing process heat source for the system; The downdraft gasifier can work well with the internal combustion engine due to its low tar content, and is suitable for distributed gasification power generation under 1MW.

根據國內氣化耦合運行情況估算，耦合發電需要達到一定規模才具有較高的經濟效益，折算機組發電容量至少約15MW以上。同時為降低對鍋爐燃燒的影響，氣化燃氣的熱值、氣量也應具有較高的穩定性。流化床氣化爐由于其良好的混合效果，均勻的溫度分布，穩定的運行效果，更適用于燃煤電廠氣化耦合發電、較大規模氣化發電、氣化合成氣制備高附加值生物燃料等場合，也適用于中小城鎮生物質（含垃圾）氣化供熱等。因此，針對燃煤電廠生物質耦合發電項目，適宜采用運行穩定性高的流化床氣化爐技術，尤其是負荷靈活度更高，原料混合更均勻的循環流化床。

According to the estimation of domestic gasification coupling operation, the coupling power generation needs to reach a certain scale to have high economic benefits, and the converted unit power generation capacity is at least about 15 MW. At the same time, in order to reduce the impact on boiler combustion, the calorific value and gas volume of gasification gas should also have high stability. Due to its good mixing effect, uniform temperature distribution and stable operation effect, the fluidized bed gasifier is more suitable for coal-fired power plant gasification coupling power generation, large-scale gasification power generation, gasification of synthetic gas to produce high value-added biofuel and other occasions, and also suitable for small and medium-sized cities and towns biomass (including garbage) gasification heating. Therefore, for the biomass coupling power generation project of coal-fired power plant, it is most suitable to adopt the fluidized bed gasifier technology with high operation stability, especially the circulating fluidized bed with higher load flexibility and more uniform raw material mixing.

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