Case Study Process Analytics in Ethylene Oxide and Ethylene Glycol Plants Chemical Industry
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Ethylene Oxide (EO)
Ethylene oxide, C2H4O, under normal conditions, is a colorless, flammable gas. It is very toxic and carcinogen. Industrial production started in 1925 using the chlorohydrin process and was improved in 1931 by introducing the much more economic direct catalytic oxidation method. Currently, almost all ethylene oxide production plants are based on the direct oxidation process with air or oxygen using a silver based catalyst. CO 2 and water are produced as by-products of the reaction.
Because EO reacts readily with many chemicals, it is one of the most versatile intermediates in the production of several industrial chemicals, the most notable of which is ethylene glycol. It is also used as a sterilant for medical equipment. However, most of it is converted into products such as fibers, foils, bottles, plasiticizers, solvents, antifreezes, cosmetics, sport articles, CDs etc.
Ethylene Glycol (EG)
Ethylene glycol (C2H4(OH)2) is produced from ethylene oxide through a catalytic reaction with water at higher temperature resulting in a yield of mono-ethylene glycol (MEG), known as glycol, and the by-products di-ethylene glycol (DEG) and tri-ethylene glycol (TEG).
Ethylene glycol is commonly used as an antifreeze agent in automobile cooling systems. It is also used in deicing solutions for aircraft and boats. Other uses include solvents for the paint and plastic industry, and hydraulic brake fluids. In pure form it is a colorless clear liquid with a sweet taste and a slightly syrupy texture. If ingested, ethylene glycol can damage the kidneys, heart and nervous system.
Integrated EO/EG plants
Modern EO/EG plants are highly integrated units where part or all of the EO produced in the EO section can be recovered as glycols, if desired, in the glycol section. Plant integration allows for significant savings in utilities as well for the recovery of all bleed streams as high-grade-products instead of lower grade products in the case of non-integrated plants.
usa.siemens.com/analyticalproducts Ethylene Oxide and Ethylene Glycols
Ethylene oxide production
Ethylene The major production steps of the oxygen- 1 Ethylene 7 CO based EO process are: 2 oxide r Oxygen 8 6
• Ethylene (acc. to IUPAC: Ethene) and Mixe oxygen are mixed with recycle gas and, Plant 2 removal removal after adding a moderating substance 2 2 area CO Chloroethane CO
such as chloro-ethane, fed into a multi- EO purification 9 tubular reactor. There, ethylene oxide Natural gas 5 Crude EO (EO) is selectively produced utilizing a 3 silver-based catalyst at 200 to 300 °C 8
and 10-20 bar. Along with ethylene r
oxide (80-85 %), CO2, H2O and heat are Steam r Acqueous EO to generated. Reaction heat is recovered by Stripper glycol section Reacto boiling water at elevated pressure on the Water EO absorbe reactors shellside. It is used at different locations of the plant. 4 + ½ O C H O • EO contained in the reactor product gas 2 2 4 CH = CH enters the EO absorber section where EO 2 2 Cycle gas + 3 O 2 CO + 2 H O is scrubbed from the gas by water. The 2 2 2 EO-containing water is concentrated by stripping producing crude EO which is Fig. 1: Ethylene oxide production process with measuring points (see details in table 1) suitable for feeding directly to a glycol producing plant. When pure EO is the desired final product, the crude EO is fed Natural gas, however, is commonly CO2 and water will occur explosively. to a purification column. contaminated with gaseous sulfur Process operation is desired under • The cycle gas leaving the absorber is fed compounds that are known as poison to conditions which will maximize the to the CO2 removal section, where CO2 the silver catalysts. conversion of ethylene to ethylene oxide (a by-product of the EO reaction) is • Catalyst selectivity is an important yet avoid safety problems. In order to find recovered. Some of the CO2 remains in parameter in EO production and should such an optimum, gases such as nitrogen the cycle gas and returns to the EO be as high as possible. Usually, during and methane are fed to the cycle gas and reactor. catalytic processes, other competing mixed with the reaction by-product reactions can take place, and reactants carbon dioxide, and argon, which enters as Process constraints are converted into undesired products. an impurity in the oxygen feed. The goal is The ratio between desired products and to find an optimum mixture which permits Various constraints exist regarding safe the undesired products is called catalyst operation of the process at maximum operation, product quality and plant selectivity. Catalyst selectivity is concentrations of oxygen and ethylene efficiency in running and optimizing the optimized by adding moderating thus increasing the selectivity of the EO production process: substances such as chloro-ethane. ethylene present to ethylene oxide and, on the other side prevents from the danger of • Oxygen is required as reactant to run Control of cycle gas composition explosion. the process and added to the cycle gas. However, at a certain concentration The desired product ethylene oxide Process analyzer are used to find this level (known as flammable limit) in the represents only a relatively small optimum mixture and to keep the gas gas mixture, oxygen will cause the percentage of the total effluent stream concentrations at the predetermined levels danger of a gas explosion. Therefore, leaving the reactor. The remainder of the during the process. See table 1 for the content of oxygen in the cycle gas reactor effluent comprises several diluents measuring details. must be monitored continuously with and reaction by-products. The task of high accuracy and reliability. the diluents is to prevent the gas mixture • Methan is able to increase the to reach unwanted combustibility levels flammable limit (which is treated as during the reaction. If the flammability positive effect) and, hence, is added to limit is reached or exceeded, the cycle gas in the form of natural gas. the complete oxidation of ethylene to
2 Ethylene glycol production Sampling Point Measuring Measuring Meas. Siemens Sampling Stream Task Components Range Analyzer The aqueous EO solution from the 1 Ethylene feed Ethylene purity to avoid C2H2 % MAXUM II ethylene oxide production section is sent catalyst poisoning S compounds to the gylcol section. There, ethylene glycol (MEG, Monoethylene glycol) is 2 Cycle gas Process control CO 0 ... 5 MAXUM II produced from EO by reacting it with 2 after mixer CH 0 ... 80 water at a 10 to 1 ratio of water to EO. 4 C2H4 0 ... 40 This excess of water helps to reduce C2H6 0 ... 2 by-product formation. Some higher glycols C2H4O 0 ... 3 are produced as co-products: diethylene N2 0 ... 20 glycol (DEG) and triethylene glycol (TEG). Ar/O2 0 ... 25 The reactor product is sent to a multi- H2O 0 ... 3 effect evaporation train for removal of the C2H4 0 ... 40 ULTRAMAT 6 water from the glycols in three successive CO2 0 ... 5 stages. The glycols are then sent to the Explosion protection O2 0 ... 12 OXYMAT 6 fractionation train where the MEG, DEG (LEL monitoring) O2 0 ... 12 OXYMAT 6 and TEG products are recovered and O2 0 ... 12 OXYMAT 6 purified. 3 Cycle gas Cycle gas composition Cl-HCs MAXUM II at reactor inlet CI-Hcs Final product samples are collected from the overhead or side stream of the 4 Cycle gas at Process control CO 0 ... 5 MAXUM II purification towers (fractionators). A 2 reactor outlet CH 0 ... 80 variety of process analysis are performed, 4 C2H4 0 ... 40 including water content, MEG, DEG or TEG C2H6 0 ... 2 (see table 2). Other measurements are C2H4O 0 ... 3 color, acidity, aldehyde impurity content N2 0 ... 20 and TOC (fig. 2). The product must meet Ar/O2 0 ... 25 sales specifications prior to being released H2O 0 ... 3 for shipment to customers. Otherwise the Explosion protection O2 0 ... 12 OXYMAT 6 product is normally reprocessed. (LEL monitoring) O2 0 ... 12 OXYMAT 6 O2 0 ... 12 OXYMAT 6
5 EO absorber Cycle gas composition: C2H4 0 ... 40 MAXUM II overhead Process control C2H6 0 ... 2 C2H4O 0 ... 0,05 Ar/O2 0 ... 30 CO2 0 ... 30 H2O 0 ... 10 6 EO product Product quality Formaldehyde MAXUM II Acetaldehyde
C2H4, CO2, H2O
7 CO2 absorber Cycle gas composition C2H4 0 ... 40 MAXUM II overhead C2H6 0 ... 2 CvH4O 0 ... 0,05 Ar/O2 0 ... 30 CO2 0 ... 30 H2O 0 ... 10 8 EO to glycol Aldehyde content Aldehyde TPA section
9 Plant area Waste water monitoring EO in water MAXUM II TOC TPA
Fig. 2: TOC system (ULTRAMAT 6 Table1: Ethylene oxide process, measuring points (TPA: Third Party Analyzer) based third party analyzer)
3 Process Gas Chromatography
The MAXUM gas chromatograph fullfills the requirements for glycols quality control Aqueous Recycle water perfectly: ethylene oxide Steam Water MEG DEG TEG
• Accurate analysis by optimized injection: Water Injection module with best evaporization 3 characteristics for high boiling samples (MEG, boiling point 194-205°C, DEG: Plant 242-247°C, TEG: 278°C) avoid area discrimination effect or hydration to r r water. 4
• Repeatable analysis by interference free Reakto Reacto separation. Safe separation of trace Evaporator Evaporator Evaporator Fractionator Fractionator Fractionator Fractionator components is performed by elimination of main components by heart-cut. Used 1 2 analyitcal tools: Siemens live switching in combination with capillary columns. MEG/DEG/TEG: Monoethylene glycol / Diethylene glycol / Triethylene glycol Verification of the results by additional control parameter: cut-rest of main component, GC oven and ambient temperature. The excellent measuring Fig. 3: Ethylene glycols production process stability, caused by the outstanding MAXUM hardware, is evident from fig. 4. • Extended calibration cycles (typically Sampling Point Measuring Measuring Measuring Siemens > 6 weeks) by on-line calibration using Sampling Stream Purpose Components Ranges Analyzer closed cylinders. No enrichment with 1 MEG fractionator Quality control DEG, TEG Medium MAXUM atmospheric moisture occurs in bottom MEG Water in MEG ppm level (Oven 1) comparison to laboratory calibration 2 DEG fractionator Quality control MEG, TEG Medium MAXUM principle. bottom DEG Water in DEG ppm level (Oven 2) • Inert capillary column systems to 3 TEG fractionator Quality control DEG, TEG Medium to MAXUM analyze traces of formalehydes and overhead TEG Water in TEG high ppm level other highly reactive components. 4 Plant area Waste water and TOC in water TPA condensate High-precision O2/Ar measurement monitoring through combined data processing with OXYMAT analysis results; see next page. Table 2: Ethylene glycols process, measuring points MEG = Monoethylene glycol DEG = Diethylene glycol TEG = Triethylene glycol TEEG = Tetraethylene glycol TOC = Total Organic Carbon TPA = Third Party Analyzer
Fig. 4: Stability of MAXUM PGC system Fig. 5: Ethylene glycol plant (INEOS Worringen, Germany)
4 OXYMAT 6 Ensures Plant Safety
Composition of the reaction gas Gain in allowable O2 concentration Flammable limit The EO reaction gas is a mixture of The danger of a gas explosion arises combustible, oxidizing and inert gases and as the oxygen concentration comes made of O2 and C2H4 along with various closer to the LOV value. Considering the Gas mixtures consisting of diluent ingredients. Due to the flammable standard deviation values of available combustible, oxidizing, and inert nature of oxygen, the ethylene production oxygen analyzers (fig. 6), the analyzer gases are only flammable under process relies on precise and accurate with a lower standard deviation (shown certain conditions. Flammable control of oxygen, and particularly, the in blue) will allow a higher oxygen limits define the proportion of "Limiting Oxygen Value" (LOV) or concentration and thus a higher process combustible components in a gas "Maximum Allowable Oxygen yield than an analyzer with a higher mixture, between which limits this Concentration" (MAOC). The LOV is the standard deviation (shown in brown). mixture is flammable. The lower oxygen concentration at which a flammable limit (LFL) describes the combustion reaction will propagate OXYMAT 6 leanest mixture that is still through the ethylene oxide process gas. flammable, while the upper Hence, using too much oxygen can result OXYMAT 6 is well known for its flammable limit (UFL) gives the in a catastrophic ignition, while using too outstanding features in reliability and richest flammable mixture. little will result in poor yield. To control stability with a very low standard Increasing the fraction of inert this critical situation independent reactor deviation. It is specified by many chemical gases in a mixture raises the LFL inlet and outlet oxygen analyzers are companies as preferred analyzer for and decreases UFL. Temperature used for oxygen monitoring and automatic this demanding application. OXYMAT 6 and pressure also influences safety shutdown and isolation of reliably ensures process safety and, at flammability limits. Higher oxygen feeds. the same time, allows for best possible temperature results in lower LFL process yield and cost reduction. and higher UFL, while greater Typically, a certain offset from the LOV is pressure increases both values. defined (fig. 6) as safety margin. If the The measuring principle uses two gases: The effect of pressure is very small. inlet oxygen concentration exceeds this a reference gas, typically nitrogen or air, LOV offset, the reactor must be shut and the sample gas. The reference gas down immediately to ensure that the (shown in green, fig. 7) is introduced channel. Because the two channels are safety margin is maintained. The size of into the sample cell through two channels. connected, the pressure difference, the offset depends on the system The reference gas stream on the right- which is proportional to the oxygen geometry and other parameters. For hand side (intensive green) meets the concentration, causes a cross flow, which example, the shut down could be triggered sample gas within the area of a magnetic is converted into an electric signal by a as the oxygen concentration exceeds field. microflow sensor. Through suitable LOV-2 vol%. Therefore it is crucial to selection of the reference gas the zero monitor and control oxygen concentration The oxygen molecules (shown as blue point can be elevated physically with at the reactor with highest degrees of beats) are drawn to the right, generating elevated oxygen concentration, e.g. accuracy and reliability. a pressure to the right reference gas 98-100% oxygen for purity monitoring.
O2 concentration of the process gas Reference gas channels Gain in allowable
O2 concentration Limiting Oxygen Value (LOV) by using OXYMAT 6 Microflow sensor for measurement Safety offset level OXYMAT 6 Other O2 analyzer Sample gas inlet
Magnetic field Sample cell
Fig. 6: Gain in allowable oxygen concentration Fig. 7: Measuring principle OXYMAT 6
5 Siemens Process Analytics at a Glance Product overview
Siemens Process Analytics is a leading provider of process analyzers and process analysis systems. We offer our global customers the best solutions for their applications based on innovative analysis technologies, customized system engineering, sound knowledge of customer applications and professional support. And with Totally Integrated Automation (TIA). Siemens Process Analytics is your qualified partner for efficient solutions that integrate process Fig. 8 Series 6 gas analyzer (rack design) analysers into automations systems in the process industry.
From demanding analysis tasks in the chemical, oil and gas and petrochemical Fig. 12 MAXUM edition II Process GC industry to combustion control in power plants to emission monitoring at waste incineration plants, the highly accurate and reliable Siemens gas chromatographs and continuous analysers will always do the job.
Siemens Process Analytics offers a wide and innovative portfolio designed to meet all user requirements for comprehensive products and solutions.
Our Products Fig. 9 Series 6 gas analyzer (field design) Fig. 13 MicroSAM Process GC The product line of Siemens Process Analytics comprises
• extractive and in-situ continuous gas analyzers (fig. 8-11) • process gas chromatographs (fig. 12-13) • sampling systems • auxiliary equipment
Analyzers and chromatographs are available in different versions for rack or field mounting, explosion protection, Fig. 10 LDS 6 in-situ laser gas analyzer Fig. 14 SITRANS CV Natural Gas Analyzer corrosion resistant etc.
A flexible networking concept allows interfacing to DCS and maintenance stations via 4-20 mA, PROFIBUS, OPC, Modbus or industrial ethernet.
Fig. 11 SITRANS SL In-situ laser gas analyser 6 Product Scope Siemens Continuous Gas Analyzers and Process Gas Chromatographs
Extractive Continuous Gas Analyzers FIDAMAT 6 Process Gas Chromatographs (CGA) The FIDAMAT 6 measures the total (Process GC) hydrocarbon content in air or even in high ULTRAMAT 23 boiling gas mixtures. It covers nearly all MAXUM edition II The ULTRAMAT 23 is a cost-effective requirements, from trace hydrocarbon MAXUM edition II is very well suited multicomponent analyzer for the detection in pure gases to measurement to be used in rough industrial environments measurement of up to 3 infrared of high hydrocarbon concentrations, and performs a wide range of duties in the sensitive gases (NDIR principle) plus even in the presence of corrosive gases. chemical and petrochemical industries and oxygen (electrochemical cell). The refineries. MAXUM II features e. g. a ULTRAMAT 23 is suitable for a wide ULTRAMAT 6 flexible, energy saving single or dual oven range of standard applications. The ULTRAMAT 6 uses the NDIR measuring concept, valveless sampling and column Calibration using ambient air eliminates principle and can be used in all applications switching, and parallel chromatography the need of expensive calibration gases. from emission monitoring to process using multiple single trains as well as a control even in the presence of highly wide range of detectors such as TCD, FID, CALOMAT 6/62 corrosive gases. ULTRAMAT 6 is able to FPD, PDHID, PDECD and PDPID. The CALOMAT 6 uses the thermal measure up to 4 infrared sensitive conductivity detection (TCD) method to components in a single unit. MicroSAM measure the concentration of certain MicroSAM is a very compact explosion process gases, preferably hydrogen.The ULTRAMAT 6 / OXYMAT 6 proof micro process chromatograph. CALOMAT 62 applies the TCD method as Both analyzer benches can be combined Using silicon-based micromechanical well and is specially designed for use in in one housing to form a multi-component components it combines miniaturization application with corrosive gases such as device for measuring up to two IR with increased performance at the same chlorine. components and oxygen. time. MicroSAM is easy to use and its rugged and small design allows mounting OXYMAT 6/61/64 right at the sampling point. MicroSAM The OXYMAT 6 uses the paramagnetic In-situ Continuous Gas Analyzers features drastically reduced cycle times, measuring method and can be used (CGA) provides valveless sample injection and in applications for process control, column switching and saves installation, emission monitoring and quality LDS 6 maintenance, and service costs. assurance. Due to its ultrafast response, LDS 6 is a high-performance in-situ the OXYMAT 6 is perfect for monitoring process gas analyzer. The measurement SITRANS CV safety-relevant plants. The corrosionproof (through the sensor) occurs directly in SITRANS CV is a micro process gas design allows analysis in the presence of the process stream, no extractive sample chromatograph especially designed for highly corrosive gases. The OXYMAT 61 is line is required. The central unit is reliable, exact and fast analysis of natural a low-cost oxygen analyser for standard separated from the sensor by using fiber gas. The rugged and compact design applications. The OXYMAT 64 is a gas optics. Measurements are carried out in makes SITRANS CV suitable for extreme analyzer based on ZrO2 technology to realtime. This enables a pro-active control areas of use, e.g. off-shore exploration measure smallest oxygen concentrations of dynamic processes and allows or direct mounting on a pipeline. The in pure gas applications. fast, cost-saving corrections. special software "CV Control" meets the requirements of the natural gas market, e.g. custody transfer.
7 Siemens Process Analytics – Solutions
Analyzer System Manager (ASM)
Industrial Ethernet
Gas Chromatographs
Fig. 15 Analyzer house (shelter) Continuous Gas Analyzers Serial Link DCS: DistributedControl System ASM: Analyzer System Manager Process Control Maintenance CEMS:Continuous Emission Monitoring System DCS Integration: ASM Modbus 4-20 mA PROFIBUS Central 3rd Party Analyzer Industrial Ethernet Maintenance Access OPC via Ethernet
Fig. 17 Communication technologies
Single Device System Analyzer networking for data communication
Decentralized Centralized Engineering and manufacturing of process analytical solutions increasingly comprises "networking". It is getting Continuous ThirdParty Field Shelter, a standard requirement in the process Process GC Gas analyzer Analyzer Installation CEMS industry to connect analyzers and analyzer systems to a communication network to provide for continuous and direct data transfer from and to the Fig. 16 Networking for DCS integration and maintenance support analysers. The two objectives are (fig. 16). • To integrate the analyzer and analyzer Analytical solutions are always driven by We rely on many years of world-wide systems seamless into the PCS / DCS the customer’s requirements. We offer experience in process automation and system of the plant an integrated design covering all steps engineering and a collection of specialized and from sampling point and sample knowledge in key industries and • To allow direct access to the analyzers preparation up to complete analyzer industrial sectors. We provide Siemens or systems from a maintenance cabinets or for installation in analyzer quality from a single source with a station to ensure correct and reliable shelters (fig. 15). This includes also signal function warranty for the entire system. operation including preventive or processing and communications to the predictive maintenance (fig. 17). control room and process control system. Read more in chapter "Our services". Siemens Process Analytics provides networking solutions to meet the demands of both objectives.
8 Siemens Process Analytics – Our Services
Siemens Process Analytics is your competent and reliable partner worldwide for Service, Support and Plant life cycle Consulting.
Planning & Engineering & Installation & Operation & Modernization Our rescources for that are Design Development Commissioning Maintenance
• Expertise Online Support As a manufacturer of a broad variety FEED for Process Analytics of analyzers, we are very much experienced in engineering and Engineering manufacturing of analytical systems and Installation and commissioning analyzer houses. We are familiar with Repairs and spare parts communication networks, well trained in service and maintenance and familiar Field service with many industrial processes and Service contracts industries. Thus, Siemens Process Optimization and modernization Analytics owns a unique blend of overall analytical expertise and experience. Technical Support • Global presence Training With our strategically located centers of competence in Germany, USA, Singapore, Dubai and Shanghai, we are Fig. 18 Portfolio of services provided by Siemens Process Analytics globally present and acquainted with all respective local and regional FEED for Process Analytics Whether you are plant operators requirements, codes and standards. or belong to an EPC Contractor you All centers are networked together. Front End Engineering and Design will benefit in various ways from (FEED for PA) is part of the planning and FEED for Process Analytics by Siemens: Service portfolio engineering phase of a plant construction or modification project and is done after • Analytics and industry know how Our wide portfolio of services is conceptual business planning and prior to available, right from the beginning segmented into Consulting, Support and detail design. During the FEED phase, best of the project Service. It comprises really all measures, opportunities exist for costs and time • Superior analyzer system performance actions and advises that may be required savings for the project, as during this with high availability by our clients throughout the phase most of the entire costs are defined • Established studies, that lead to entire lifecycle of their plant: and changes have least impact to the realistic investment decisions • Site survey project. Siemens Process Analytics holds a • Fast and clear design of the analyzer • Installation check unique blend of expertise in analytical system specifications, drawings and • Functionality tests technologies, applications and in providing documentation • Site acceptance test complete analytical solutions to many • Little project management and • Instruction of plant personnel on site industries. coordination effort, due to one • Preventive maintenance responsible contact person and • On site repair Based on its expertise in analytical less time involvement • Remote fault clearance technology,application and engineering, • Additional expertise on demand, • Spare part stock evaluation Siemens Process Analytics offer a wide without having the costs, the • Spare part management scope of FEED services focused on effort and the risks of building • Professional training center analyzing principles, sampling up the capacities • Process optimisation technologies, application solutions as well • Lowest possible Total Costs of • Internet-based hotline as communication system and given Ownership (TCO) along the • FEED for Process Analytics standards (all related to analytics) to lifecycle regarding investment • Technical consullting support our clients in maximizing costs, consumptions, utilities performance and efficiency of their supply and maintenance projects.
9 10 Notes:
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