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密相输送（Dense Phase Conveying）是气力输送的一种形态：用 1.5~3.5 bar 的压缩空气，以 3~10 m/s 的低气速，把粉粒料以高浓度（固气比通常 15~50 kg/kg）推送通过管道。物料在管内不是悬浮飞舞，而是以栓流、沙丘流或集团流的形式整体前移。
和稀相输送相比，密相输送用更高的压力换更低的速度。速度降下来之后，三件事同时受益：物料破碎和拉丝减少、管道磨损减轻、单位输送量的耗气量下降。代价是系统压力等级升高，供料点要承受 1.5~3.5 bar 的压差，对供料设备和密封的要求完全不同。
| 对比项 | 稀相输送 | 中间相输送 | 密相输送 |
|---|---|---|---|
| 气速量级 | 15~30 m/s | 8~16 m/s | 3~10 m/s |
| 工作压力 | 常压~0.5 bar | 0.5~1.5 bar | 1.5~3.5 bar |
| 固气比 | 1~8 kg/kg | 8~15 kg/kg | 15~50 kg/kg（仓泵可更高） |
| 物料状态 | 均匀悬浮 | 部分沉积、脉动推进 | 栓流/集团流 |
| 破碎与拉丝 | 高 | 中 | 低 |
| 管道磨损 | 高 | 中 | 低 |
| 典型供料设备 | 普通旋转阀、文丘里 | 旋转阀+压力控制 | 仓泵（发送罐）、高压旋转阀 |
| 适用距离 | 短距离 | 中距离 | 中长距离 |
三种形态没有优劣之分，只有与物料和工况的匹配与否。中间相的定位与判据在站内另一篇有完整说明：中间相气力输送（STRANDPHASE）是什么。本文聚焦密相。
一套完整的密相输送系统包含五个部分：
图：密相输送系统现场——供料段压力表与高压输送管道
这是密相输送选型的核心决策点。
| 对比项 | 仓泵（发送罐） | 高压旋转阀连续供料 |
|---|---|---|
| 供料方式 | 批次式：装料→加压→输送→泄压循环 | 连续式：叶轮旋转连续喂料 |
| 系统压差 | 1.5~3.5 bar，可更高 | 1.5~3.5 bar（高压系列） |
| 产能特性 | 单批次量固定，靠循环频率提产 | 产能连续可调，变频匹配 |
| 锁气要求 | 靠进料阀/出料阀时序密封 | 靠 0.05~0.10 mm 叶片间隙+多级轴封 |
| 适用场景 | 长距离、大产能、单点供料 | 多点供料、连续工艺、需要精确计量 |
| 维护重点 | 阀门密封件、圆顶阀 | 叶片间隙、轴封、排气口 |
选仓泵的情况：输送距离超过 300 米、产能需求大、物料流动性好且允许批次供料。
选高压旋转阀的情况：工艺要求连续供料（如挤出机前端、配料线上游）、需要在压差下精确计量、多供料点切换。3.5 bar 级高压旋转阀的选型参数、间隙控制与漏气量核算方法，见高压旋转阀选型专题与高压旋转阀厂家与供应商。
工程上也有组合方案：主输送用仓泵保证长距离能力，末端分配点用旋转阀做二次计量。
固气比（料气质量比）是密相的定义性参数。固气比达到 15 kg/kg 以上通常才归入密相；8~15 kg/kg 属于中间相区间，密相常见运行区间为 15~50 kg/kg。固气比越高，单位产量的耗气量越低，但对物料流动性和管道布置的要求越高，栓流不稳定时会出现脉动堵管。
密相的气速窗口是 3~10 m/s。低于沉积速度会堵管，高于窗口上限则退化到中间相、失去护料与节能意义。设计时按出口端气速反推，全程气速曲线要逐段核算，不是只看风机出口一个点。
密相供料点压差常见 1.5~3.5 bar。这个压差几乎全部落在供料设备上：选旋转阀供料时，阀门额定压差建议按系统工作压差的 1.25 倍以上选取，并核算高压差下的启动扭矩（可达常压工况的 3~5 倍）。
采用旋转阀供料时，间隙漏气直接吃掉风机风量。参考量级：DN300 阀在 3.5 bar 压差、0.10 mm 间隙下，漏气量约 210~320 m³/h，占风机风量的 15%~22%；间隙磨损到 0.25 mm，漏气量升到 520~800 m³/h，占比 35%~50%。气源选型必须把这部分泄漏计入，否则系统表现为"风量永远不够"。
适合密相的物料画像：
不适合硬上密相的情况：物料易吸潮结块且无法伴热、产能很小且距离很短（稀相更简单便宜）、现场无法提供稳定 3 bar 以上气源。
上海科全技术团队核心成员参与过 40 万吨/年 PVC、40 万吨/年 LDPE、40 万吨/年 HDPE 等大型聚烯烃装置的气力输送系统设计。这类装置的典型工况是 1.5~3.5 bar 密相，物料价值高、连续运行时间长、对金属污染零容忍。
在俄罗斯 40 万吨/年 PE 装置上，科全自研 GVH 系列高压旋转阀完成了 3.5 bar(g) 高压差工况的进口替代并通过验收：叶片间隙控制在 0.05~0.10 mm 并可调，侧盖内布置机械密封+油封+迷宫+轴气封的多级密封链，强制配置排气口（Vent Port）释放格腔携气。验收指标里，持续允许压差与该压差下的泄漏率都作为可测项写入协议，这也是判断任何高压供料设备供应商的两条硬标准。
Q1：密相输送和稀相输送有什么区别？
气速、压力、浓度三方面都不同。稀相气速 15~30 m/s、压力常压~0.5 bar、固气比通常在 8 以下，物料均匀悬浮；密相气速 3~10 m/s、压力 1.5~3.5 bar、固气比 15~50，物料以栓流形式推进。稀相设备简单适合短距离，密相护料、节能、磨损低，适合中长距离和易碎物料。
Q2：密相输送的固气比多少算合理？
密相与中间相的工程分界线是 15 kg/kg，常见运行区间 15~50 kg/kg。不是越高越好：超过物料流动性允许的范围，栓流会失去稳定性，表现为压力大幅脉动甚至堵管。合理值由物料实测（堆积密度、休止角、透气性）和管道布置共同决定。
Q3：密相输送选仓泵还是旋转阀供料？
看三件事：供料要不要连续（连续选旋转阀）、距离是不是特别长（超长距离仓泵压力上限更高）、要不要精确计量（选旋转阀）。组合方案也常见。具体参数核对建议提供输送量、距离、物料特性后由技术团队计算。
Q4：3.5 bar 高压旋转阀在密相输送中起什么作用？
同时承担三件事：把物料定量喂入高压管道、阻止管道压缩空气反窜回料仓、在持续压差下维持锁气。它要求 0.05~0.10 mm 的可调叶片间隙、多级轴封加轴气封、强制排气口，不能用 1.5 bar 标准阀改造替代。
Q5：密相输送系统比稀相省多少能耗？
方向是省的，幅度看工况。固气比从稀相的 10 提到密相的 30，单位产量的输送气量约为原来的三分之一；但密相需要更高的供气压力，空压机能耗曲线不同。综合电耗需要按具体输送量、距离、气源效率逐项核算，建议以设计院的工艺包数据为准。
Q6：粒料密相输送末端为什么要配除粉器？
密相虽然大幅降低破碎和产粉，但上游来料本身含粉、输送过程仍有少量新生粉尘。末端接收仓配除粉器可把成品含粉量控制在客户验收线以内，避免"输送系统合格、成品含粉超标"的尴尬。除粉器选型见站内除粉器专题。
密相输送系统的供料方式选择、气源核算、高压旋转阀选型与漏气量复算，可把以下参数发给我们做免费工艺核算：物料名称与堆积密度、输送量（t/h）、水平/垂直距离与弯头数量、可用气源压力、目标输送相态。
上海科全工程技术有限公司
官网：www.shconque.com
电话：021-67893550 ／ 18916616687
传真：021-67893550
邮箱：shconque@163.com
地址：上海市松江区石湖荡镇塔汇路609号（注册）／ 松江区广富林路658弄4号楼705室（办公）
同一个密相输送主题，按不同读者的关注点做了三版改写，内容互补，可按需查阅：
需要按自己的工况做核算，可对照本文第九节列出的参数清单，把物料、输送量、距离与气源压力发给我们。
Dense-phase conveying is a mode of pneumatic conveying in which 1.5–3.5 bar compressed air moves powders and pellets at a low velocity of 3–10 m/s and a high solids loading (typically 15–50 kg/kg). The material does not fly in suspension; it travels through the pipe as plugs, dunes or slugs.
Compared with dilute phase, dense phase trades pressure for velocity. Lower velocity brings three benefits at once: less breakage and angel hair, less pipe wear, and lower air consumption per tonne conveyed. The price is a higher pressure rating — the feeding point must withstand a 1.5–3.5 bar differential, which places completely different demands on the feeder and its sealing.
Dense-phase conveying uses 1.5–3.5 bar compressed air at 3–10 m/s to push powders and pellets at high concentration through a pipeline. The material moves as a plug, dune or slug rather than as a cloud of suspended particles. Because the particles travel slowly and stay close together, collision energy at the pipe wall is low, and the same throughput can be achieved with far less air than in dilute phase.
| Item | Dilute phase | Intermediate phase | Dense phase |
|---|---|---|---|
| Air velocity | 15–30 m/s | 8–16 m/s | 3–10 m/s |
| Operating pressure | Atmospheric to 0.5 bar | 0.5–1.5 bar | 1.5–3.5 bar |
| Solids loading | 1–8 kg/kg | 8–15 kg/kg | 15–50 kg/kg (higher with blow tanks) |
| Material state | Uniform suspension | Partial deposition, pulsating flow | Plugs or slugs |
| Breakage and angel hair | High | Medium | Low |
| Pipe wear | High | Medium | Low |
| Typical feeder | Conventional rotary valve, venturi | Rotary valve with pressure control | Blow tank (send vessel), high-pressure rotary valve |
| Typical distance | Short | Medium | Medium to long |
None of the three is inherently better; the question is whether it matches the material and the duty. The intermediate-phase position and its criteria are explained in a separate article on this site: Intermediate-Phase Pneumatic Conveying (STRANDPHASE). This article focuses on dense phase.
A complete dense-phase conveying system has five parts:
This is the central decision in dense-phase selection.
| Item | Blow tank (send vessel) | Continuous high-pressure rotary valve |
|---|---|---|
| Feeding mode | Batch: fill, pressurise, convey, vent | Continuous: the rotor meters material |
| System differential | 1.5–3.5 bar, can be higher | 1.5–3.5 bar (high-pressure series) |
| Capacity | Fixed batch size; throughput via cycle rate | Continuously adjustable, VFD matched |
| Air lock | Inlet and outlet valve sequencing | 0.05–0.10 mm blade clearance plus multi-stage shaft seal |
| Best fit | Long distance, high capacity, single feed point | Multiple feed points, continuous process, accurate metering |
| Maintenance focus | Valve seals, dome valve | Blade clearance, shaft seal, vent port |
Choose a blow tank when the distance exceeds 300 m, the capacity is high, the material flows freely and batch operation is acceptable.
Choose a high-pressure rotary valve when the process requires continuous feed (for example upstream of an extruder or on a batching line), accurate metering under differential pressure is needed, or several feed points must be switched. Selection parameters, clearance control and leakage calculation for 3.5 bar valves are covered in High-Pressure Rotary Valve Selection and High-Pressure Rotary Valve Manufacturers.
A combined scheme is also common: blow tanks provide the long-distance capability on the main line, while rotary valves handle secondary metering at distribution points.
Solids loading (mass of solids per mass of air) is the defining parameter of dense phase. Above 15 kg/kg a system is normally classed as dense phase; 8–15 kg/kg is the intermediate-phase band, and dense-phase systems typically run at 15–50 kg/kg. Higher loading cuts air consumption per tonne but demands better material flowability and pipe layout; when plug flow becomes unstable, the result is pressure pulsation and blockage.
The dense-phase window is 3–10 m/s. Below the saltation velocity the line blocks; above the upper limit the flow degenerates into intermediate phase and loses both the gentle handling and the energy benefit. Design from the outlet velocity backwards and check the velocity profile section by section, not just at the blower outlet.
1.5–3.5 bar at the feeding point is typical. Almost all of it falls across the feeder: with a rotary valve, select a valve rated at least 1.25 times the working differential and check the starting torque at the high differential, which can be 3–5 times the atmospheric value.
With rotary-valve feeding, clearance leakage eats directly into blower capacity. Reference magnitudes: a DN300 valve at 3.5 bar and 0.10 mm clearance leaks about 210–320 m³/h, or 15–22% of blower flow; at 0.25 mm the figure rises to 520–800 m³/h, or 35–50%. Air-supply sizing must include this leakage, otherwise the system behaves as if the air flow is never enough.
Suitable material profiles:
Dense phase is a poor fit when the material absorbs moisture and cakes without heat tracing, when throughput is very small over a very short distance (dilute phase is simpler and cheaper), or when the site cannot provide a stable air supply above 3 bar.
Core members of Shanghai Conque's technical team have designed pneumatic conveying systems for 400,000 t/a PVC, LDPE and HDPE plants. These duties typically run at 1.5–3.5 bar dense phase, with high-value material, long continuous runs and zero tolerance for metal contamination.
At a 400,000 t/a PE plant in Russia, Conque's in-house GVH high-pressure rotary valve completed import substitution at 3.5 bar(g) and passed acceptance. Blade clearance is adjustable within 0.05–0.10 mm; the side cover contains a multi-stage seal chain of mechanical seal, oil seal, labyrinth and shaft air seal; and a vent port is mandatory to release air carried in the rotor pockets. Both the continuous allowable differential and the leakage rate at that differential were written into the acceptance protocol as measurable items — two hard criteria for judging any high-pressure feeder supplier.
Q1: What is the difference between dense-phase and dilute-phase conveying?
Velocity, pressure and concentration all differ. Dilute phase runs at 15–30 m/s, atmospheric to 0.5 bar, with solids loading typically below 8, and the material is fully suspended. Dense phase runs at 3–10 m/s and 1.5–3.5 bar, with solids loading of 15–50, and the material moves as plugs. Dilute-phase equipment is simpler and suits short distances; dense phase protects the product, saves energy and reduces wear, and suits medium-to-long distances and friable materials.
Q2: What solids loading is reasonable for dense phase?
The engineering boundary between dense and intermediate phase is 15 kg/kg, with 15–50 kg/kg typical. Higher is not automatically better: beyond what the material's flowability allows, plug flow becomes unstable, shown by large pressure pulsation or blockage. The right value comes from material testing (bulk density, angle of repose, permeability) and pipe layout.
Q3: Should I use a blow tank or a rotary valve?
Three questions decide it: does the process need continuous feed (choose a rotary valve), is the distance very long (a blow tank has the higher pressure ceiling), and is accurate metering required (choose a rotary valve). Combined schemes are common. For specific parameters, send the throughput, distance and material data to the technical team.
Q4: What does a 3.5 bar high-pressure rotary valve do in a dense-phase system?
Three things at once: meter material into the high-pressure line, prevent compressed air from blowing back into the silo, and maintain the air lock under continuous differential. It requires 0.05–0.10 mm adjustable blade clearance, a multi-stage shaft seal with shaft air purge, and a mandatory vent port; a 1.5 bar standard valve cannot be modified to do the job.
Q5: How much energy does dense phase save compared with dilute phase?
The direction is favourable; the magnitude depends on the duty. Raising solids loading from 10 in dilute phase to 30 in dense phase reduces conveying air per tonne to about one third of the original. But dense phase needs a higher supply pressure and the compressor efficiency curve differs. Overall power consumption must be calculated item by item for the specific throughput, distance and air-supply efficiency; the design institute's process package is the reference.
Q6: Why does a pellet dense-phase line need a deduster at the receiving end?
Although dense phase greatly reduces breakage and fines generation, the incoming material already contains fines and a small amount of new dust is still created. A deduster at the receiving silo keeps the finished product within the customer's acceptance limit, avoiding the awkward case where the conveying system passes but the product's fines content does not. See the deduster article on this site.
For feed-route selection, air-supply sizing, high-pressure rotary valve selection and leakage recalculation, send the following parameters to our team for a free process check: material name and bulk density, throughput (t/h), horizontal and vertical distance, number of elbows, available air pressure, and target conveying regime.
Shanghai Conque Engineering Technology Co., Ltd.
Tel: +86 21 6789 3550 / +86 189 1661 6687
Email: shconque@163.com
Address: No. 609 Tahui Road, Shihudang Town, Songjiang District, Shanghai (registered) / Room 705, Building 4, Lane 658 Guangfulin Road, Songjiang District, Shanghai (office)
