Flow Instrumentation Solution for the Chemical Industry (Adipic Acid)
Application Description
Adipic acid is a core organic intermediate widely used in the manufacture of polymers such as nylon and polyurethane. The two prevailing routes are nitric acid oxidation of KA oil from complete benzene hydrogenation and nitric acid oxidation of cyclohexanol from partial benzene hydrogenation. Both cover the core steps of benzene hydrogenation, oxidation and crystallization separation, with metered media including cyclohexane, cyclohexene, cyclohexanol, KA oil, hydrogen, nitric acid, ammonia and process air.
Every stage runs under extreme duty: high temperature, high pressure, multiphase flow and severe corrosion. These conditions pose more than an accuracy challenge; they dictate the failure modes themselves, namely deposition and blockage, particle erosion, hydrogen embrittlement cracking, crystal build-up and signal noise. The demands placed on the stability, accuracy and durability of flow metering equipment are therefore stringent.
Application Focus
The six challenge classes below run through the whole adipic acid process. They are the primary causes of instrument failure and the boundary conditions that every selection must address.
1. Cyclohexane is viscous and deposits readily, blocking meter flow passages; benzene mixed with hydrogen forms a gas-liquid multiphase flow that is difficult to meter.
2. High temperature and pressure throughout production place extreme demands on material compatibility, structural stability and operating performance.
3. Catalyst-laden gas-solid two-phase flow erodes and wears meter internal walls severely.
4. Hydrogen generation duties carry caustic solution and chloride ions, readily causing corrosion failure.
5. In nitric acid units, the ammonia-to-process-air ratio determines oxidation efficiency and the product qualification rate.
6. Nitric acid oxidation is strongly exothermic; medium temperature and viscosity fluctuate dynamically, disturbing conventional meters and degrading measurement accuracy.
Solution Overview
Addressing these challenges, selection follows four medium-driven principles: anti-blocking and wear resistance, corrosion-resistant alloys, high-accuracy mass flow and wide-range gas metering. Together they cover every key measuring point in an adipic acid plant.
1. Cyclohexane (high viscosity, abrasive, blockage-prone)
A wedge flowmeter with dual-flange pressure tapping. The wedge throat leaves deposits nowhere to collect, and dual-flange tapping eliminates blockage-prone impulse lines, preventing deposition at source.
2. Benzene and hydrogen (flammable and explosive, with hydrogen embrittlement risk)
A standard orifice plate or an integrally forged Venturi tube. Built on seamless steel pipe and solution annealed in 316L, the body is free of residual stress, so hydrogen atoms cannot collect at stress concentrations and initiate hydrogen embrittlement cracking.
3. Catalyst-laden gas-solid two-phase media
A Venturi tube flowmeter. Smooth converging walls with no dead zones resist particle erosion; for high-wear duties the bore can be sprayed with tungsten carbide to dissipate particle energy layer by layer before it reaches the base metal.
4. Benzene hydrogenation to cyclohexene (severe high-temperature, high-pressure duty)
A differential-pressure standard orifice plate, or a multi-hole balanced flowmeter. The balanced plate is self-conditioning and fouling-resistant: its symmetric orifices flatten the flow profile before tapping, delivering 5 to 10 times the accuracy of a conventional orifice plate at one third of the permanent pressure loss, with a substantial energy saving.
5. Hydrogen and high-pressure oxygen (low flow resistance, low energy demand)
A Venturi tube flowmeter: low flow resistance and high stability suit high-purity media and reduce energy consumption in the compressor train.
6. Cyclohexane, phenol and KA oil (high specific gravity, viscous and deposition-prone)
A Coriolis mass flowmeter measures mass flow, density and temperature directly and outputs all three simultaneously, so results do not drift with temperature and no volume-to-density conversion error is introduced.
7. Ammonia (low flow, water-bearing, corrosive)
For high-accuracy duty use a Coriolis mass flowmeter in Hastelloy C (HC); for general duty, a vortex flowmeter with an HC probe and a 316L body, or a standard orifice plate. HC resists stress corrosion cracking in ammonia service.
8. Process air (wide-range fluctuating duty)
A vortex flowmeter or a thermal gas mass flowmeter. Thermal meters exceed a 1000:1 turndown and offer inline or insertion mounting, accommodating the wide load swings of the oxidation furnace.
9. Nitric acid (conductive and corrosive)
A class 0.2 electromagnetic flowmeter with PTFE or PFA lining and corrosion-resistant electrodes. Electromagnetic measurement is unaffected by fluctuations in density, viscosity, temperature and pressure, giving inherently stable performance in corrosive media.
10. Cyclohexanol micro-dosing (non-conductive, low flow, high accuracy)
A high-accuracy Coriolis mass flowmeter, paired with electromagnetic meters to achieve precise medium proportioning. Low flow at high accuracy is precisely the Coriolis strength, with measurement down to DN3 micro-flow.
Customer Value
1. Stable reaction conditions and a higher product qualification rate
2. Lower risk of instrument failure and unplanned shutdown under severe duty
3. Reduced field maintenance and spare-parts replacement cost
4. Credible measurement of material and energy consumption to support plant-level accounting
5. Stable, reliable flow signals from all key measuring points feed high-quality process data to DCS, MES and process simulation systems, supporting closed-loop control and plant digitalization.
Related Products
1. DF Series differential pressure flowmeters
Including standard orifice plates, multi-hole balanced orifice plates, nozzles, wedge elements, V-cone, Venturi tubes, segmental orifice plates and rectangular flowmeters, used for anti-blocking wedge metering of cyclohexane, Venturi metering of hydrogen and oxygen, high-temperature high-pressure throttling in benzene hydrogenation, and nitric acid oxidation control.
2.MFM Series Coriolis mass flowmeters
Mass metering of cyclohexane, phenol and KA oil, high-accuracy ammonia proportioning, cyclohexanol micro-dosing and product custody transfer.
3.MF Series electromagnetic flowmeters
Primary flow metering of nitric acid and other conductive corrosive media.
4.VFD Series vortex flowmeters
Metering of process gases including process air, ammonia, hydrogen and oxygen.
5.RFC Series metal-tube rotameters
Low-flow dosing of catalyst slurry, ammonia water and additives.
6.TFC Series turbine flowmeters
High-viscosity media and duties demanding high repeatability.