Applications ofFast Gas Analysis by Mass Spectrometryto Process Control in the Iron and Steel Industry
质谱在钢铁行业过程控制中快速气体分析的应用
Robert Wright
Thermo Electron Corporation
Abstract 摘要
This paper describes howfast on-line gas analysis by mass spectrometry is used in the iron and steel industry to optimise various processes, based on accurate and complete analysis. Steel making gas analysis is used forbetter process control and end-point determination to expedite process-turnaround. Iron making gas analysis is used to operate more efficiently and safely. Coke oven gas analysis is used to optimise the gas cleaning.Waste gases from variousprocesses are used as fuel gas,which needs to be characterised in terms of calorific value, Wobbe index and stoichiometric air requirement, butthese gases have fast changing composition. These gases are also mixed to make mixed fuel gas. Fast complete gas analysis is required to optimise the mixing of these gases to providemixed gas ofconstant calorific value (or Wobbe Index).
本文描述在钢铁行业中如何采用质谱对气体进行准确、完整的快速在线气体分析以优化不同的过程。炼钢过程中的气体分析用于更好地控制过程，确定吹炼终点以加速吹炼周期。焦炉中的气体分析用于优化气体纯化。来源于不同过程中的废气用作燃气，通过热值，华比值和按化学计量组成所需空气量表征，这些气体组成变化很快。这些气体也被混合形成混合燃气。因此采用快速全面的气体分析来优化混合过程以提供稳定华比值的混合气体。
Introduction介绍
The type of mass spectrometer used for on-line gas analysis is commonly referred to as a process mass spectrometer, or PMS. One of the world’s largest scientific instrument manufacturers, Thermo Electron Corporation, has been manufacturing process mass spectrometers for over 20 years with more than 1000 systems installed world-wide on a wide range of applications – in the chemical and petrochemical industries and in biotechnology and for research & development, as well as iron and steel. Specifically for the iron and steel industry during the past 15 years, Thermo Electron has installed over 100 mass spectrometers for gas analysis applications involving the following plants: coke ovens, blast furnace (BF), direct reduction iron (DRI), basic oxygen furnace (BOF), electric arc furnace (EAF), argon oxygen decarburization (AOD) furnace, vacuum oxygen decarburization VOD furnace and Ruhrstahl-Hausen (RH) furnace. Additionally gas analysis by PMS is used to characterise the combustion properties of fuel gas used in the iron and steel industry.
用于在线气体分析的质谱仪通常被称作过程质谱。热电公司，作为世界上最大的科学仪器厂商之一，有二十多年的过程质谱仪研究经验，超过1000台过程质谱仪系统在世界各地运行并具有广泛的应用： 化学，石化和生物科技的研发，以及钢铁工业。尤其在过去15年的钢铁行业中，超过100台过程质谱仪用于气体分析，包含：焦炉，高炉，直接还原炼铁炉，氧气顶吹转炉，电弧炉，氩氧脱碳转炉，真空氧气脱碳炉和循环法真空脱碳炉。另外过程质谱对气体的分析也可表征用于钢铁工业中的燃料的燃烧特性。
The gas analysis measurements are fast, typically between 0.3 and 1 second per component. They are accurate, typically better than 1% relative. The detection range is from 100% down to 10ppb (depending on the species and other components present). The analysis is multi-component, most systems installed are measuring between 4 and 10 different components simultaneously. It is also multi-stream – it switches from one stream to another using a multi-port valve. Of course being designed for on-line installation it is available in both general purpose & Ex hazardous area compliant versions. To configure the instrument for a variety of applications, user-friendly mass spectrometer software is provided on a PC connected to the instrument via a serial link. This PC also provides for logging and trending data, if required, and also provides for tuning and diagnostics. Communications from the mass spectrometer itself to a host computer can be via digital and/or analogue signals or by serial link using industrial standard protocols such as Modbus, Profibus or Siemens 3964R. Ethernet communication using OPC is becoming more common.
气体分析的速度快而且准确，通常每个组分的分析速度为0.3到1秒，精度优于1%。检测范围从100%到10ppb（取决于样品和样品中的其他组分）。可进行多组分分析，安装的多数系统常同时测量4到10个不同的组分。也可进行多流路测定，从一个流路到另一个流路的切换只需采用多头进样阀。当然对在线安装的设计拥有适用于安全区和危险区两种型号。通过序列接口连接仪器和计算机，使用拥有友好用户界面的软件设置以适应不同的应用要求。计算机也可提供记录和追踪数据，如需要也可提供远程调试和诊断。质谱仪和主机的通信可通过数字或模拟信号或是序列连接使用工业标准协议如Modbus, Profibus or Siemens 3964R。使用OPC可实现以太网通讯。
Sample conditioning of the gas being sampled by the PMS is similar to other process gas analysers. The gas needs filtering and pressure regulation to provide sufficient flow (typically between 0.2 and 1.0 l/min) of clean sample gas to the mass spectrometer; water is not critical, but often the gas is dried. The maintenance requirements of the PMS are not high, normal uptime is >99.8%.
过程质谱仪对气体的取样条件和其他的过程气体分析仪相似。气体需要经过过滤和压力调节以提供足够流速（0.2 - 1.0 升/分）的干净样品气进入质谱仪，气体可含水，但通常样品气是干燥的。
对质谱仪的维护要求并不高，正常的运行时间可达到>99.8%。
The main justifications for investing in a PMS instrument are the following:-
对过程质谱投资只要理由如下：
· Analysis response time is very fast (as fast as 1.5 seconds for analysis of 6 components).
分析速度快（6个组分只需1 .5秒）
· It is multi-component – all components of interest are typically measured on a single instrument.
多组分测量- 所有待测的组分可在一台仪器上测量
· It is multi-stream – multiple sample gases are measured on the same instrument
多流路测量 – 在同一台仪器上实现多路样品测量
· The high analytical performance in terms of sensitivity, stability and linearity.
具有高分析性能：极高的灵敏度，稳定性和宽的线性范围
· There is a definite cost benefit in incorporating composition gas analysis or derived data into the plant control strategy.
气体组分分析和工厂数据控制产生的经济价值和益处远远超过投资
How a Mass Spectrometer Works 质谱仪原理
There are a few basic elements to a mass spectrometer: an inlet to introduce the sample gas into the vacuum of the mass spectrometer, an ion source to convert the sample gas molecules into positively charged ions, a mass filter to separate the ions using magnetic or electric fields and a detector that quantifies the amounts of ions at different masses. Very importantly, there is a vacuum chamber with high vacuum pumps and electronics to run the mass spectrometer. Modern instruments have embedded processors to run the instrument in a completely stand-alone manner, so no user intervention is required to keep the instrument analyzing and calibrated over the 12 month period between scheduled maintenance operations.
质谱仪的几个基本组成部分：将样品引入质谱仪的进样系统，将气体分子转变为正离子的离子源，使用磁场或电场分离离子的质量分析器，对不同质量数离子定量的检测系统。拥有真空泵和电子装置的真空室质谱仪运行中重要组成部分。内置的处理器使仪器完全可以独立运行，无需人为干预便可实现12个月以上仪器自动分析和矫正。
The PMS instrument supplied by Thermo Electron for the iron and steel industry is the model VG Prima δB. The VG Prima δB uses deflection in a sector shaped magnetic field as the mass filter. There is a variable electromagnet to select the different mass ions for measurement. The magnetic field is ramped in value to step between the characteristic masses, e.g. for measuring H2, CO, N2, O2, Ar and CO2 it will first set the magnetic field to detect mass 2 ions, then mass 12 ions, then mass 14 ions, then mass 32 ions, then mass 40 ions, and then mass 44 ions. These mass ions correspond to the gases as shown in table 1 below.
VG Prima δB是热电公司为钢铁行业提供的过程质谱仪。VG Prima δB采用扇形磁场质量分析器，使用可变磁场选择不同的待测离子。磁场强度根据特征质量作步进升高，如测量H2, CO, N2, O2, Ar and CO2，首先选择磁场检测质量数为2的离子，然后是质量数为12的离子，然后是14，32，40，44。
这些离子在如下表1中列出。
Table 1: Mass ion peaks corresponding to various gases
Mass / Gas responsible for signal at this mass / Description of positive ion producing this signal2 / H2 / H2+
12 / CO + CO2 / 12C+
14 / N2 / 14N+
32 / O2 / 16O2+
40 / Ar / 40Ar+
44 / CO2 / 12C16O2+
It seen that most of the mass peaks are unique to one gas. The only exception is mass 12, which results from the C+ ion which arises from the ionisation of both CO and CO2. During calibration which measures the magnitude of the peak height for a known concentration of gas, pure CO2 is used for determining the ratio of the mass 12 peak to the mass 44 peak, so it is a simple correction to subtract the CO2 contribution to mass 12. However, there are limitations to the accuracy of this correction and a ‘rule of thumb’ is that the detection limit for CO is 2% of the CO2 concentration.
可以看出大多数质量峰和一种气体相对应。质量数为12的例外，由CO 和 CO2的离子化产生。在校正时，纯CO2用于确定质量峰为12和44的比例，因此只需减去CO2对质量数12的贡献。然而，这种校正方法的有一定的精度限制并且根据经验CO的检出限为CO2的2%。
A representation of a gas analysis mass spectrometer is shown below in figure 1.
Figure 1: Schematic representation of a gas analysis mass spectrometer
Benefit of Magnetic Sector Mass Filter 扇形磁场质量分析器的优点
Process mass spectrometers take measurements very quickly by jumping to each of the nominal mass positions. The assumption is that top of the peak coincides with the nominal mass position. However this may not be the case if the peak top is narrow and the mass scale drifts. The advantage of the VG Prima over other process mass spectrometer designs is that it uses a sector shaped magnetic field, which produces trapezoidal peak shapes with extensive peak tops. It is therefore very tolerant to drifts in the mass scale.
过程质谱仪通过跳到定义的质量位置实现快速测量。此假设基于峰顶的位置与所定义的质量位置相符合。然而，由于峰顶太窄或是质量漂移将会产生不同的结果。VG Prima优于其它过程质谱仪的设计在于其采用扇形磁场，产生的峰形为平顶的梯形峰，因此在质量范围内不易漂移。
An example appearance of a peak is shown below in figure 2.
图2为一质量峰峰形外观。
Figure 2: Peak shape from magnetic sector mass spectrometer
Overview of Iron and Steel Processes 钢铁冶炼过程总述
Below, in figure 3, is shown a representation of various processes in the iron and steel works which use gas analysis as part of their control. As a simple overview, the blast furnace needs coke from the coke plant to reduce the iron ore (iron oxide) to iron. The iron is converted into steel in the BOF using oxygen to remove impurities such as carbon. Further refining may take place in processes such as AOD, VOD or RH. Continuous casting converts the steel into billets, blooms and slabs. Reheat furnaces then melt this steel for making it into the various products such as sheets, bars, rods, coils etc. Another route to steel is from DRI to make the iron from iron ore and natural gas. The product is then used in an EAF to make steel. However, the main material used in the EAF is scrap steel.
如下图三为在钢铁冶炼过程中气体分析作为过程控制的系统图。焦炉厂中生成的焦炭在高炉中还原铁矿石（铁的氧化物）成铁。在氧气顶吹转炉中，通过氧除去碳等杂质将铁转为钢。在AOD, VOD 或 RH过程中进一步精炼。连铸将钢转变为钢柸，初轧抷和厚板。然后再热炉将钢铁融化炼成不同的产品如钢片，钢条，钢棒和钢圈等。另外一种方法是直接还原，从铁矿中炼铁和天燃气。产物被用于电弧炉中炼钢。然而，在电弧炉法中主要的原料是废钢。
Figure 3: Processes in the iron and steel works which use gas analysis
Coke Oven 焦炉
In a coke oven plant, a raw gas of high calorific value is produced as a by-product from the pyrolysis of coal (the coke product being used in a blast furnace for iron production). After purification, coke oven gas is used as fuel by other processes in the iron and steel works. A purification plant is necessary to remove problematic (naphthalene blockages), and environmentally harmful (H2S, NH3, benzene) components. On-line monitoring of H2S and O2 are often well established on coke oven plants. However, measurement of NH3, naphthalene and benzene traditionally were performed by wet chemical methods on a daily spot sample basis. However, more recently mass spectrometry has been applied to extend the range of components in purified coke oven gas being subjected to on-line monitoring. It has been found that on-line monitoring allows optimization of the scrubber plants (refs 1,2). Additionally, the mass spectrometric analysis of all the components is expanded to derive the combustion properties of the gas. This is important because this gas is used as fuel by various other processes as well as for heating the coke oven batteries themselves. These properties include calorific value, density, specific gravity, Wobbe index and stoichiometric air requirement. Such calculations enable the more efficient use of fuel and the savings can be considerable. Typical composition of coke oven gas measured by PMS is shown below in table 2.
在焦炉厂中，裂解煤的副产物为高热值的原料气体（焦炭产物在高炉中用于还原铁）。经纯化后，焦炉气体在其他钢铁冶炼过程中用作燃料。净化厂是必需的以除去干扰物（萘阻塞）和环境污染物（H2S, NH3, 苯）。在焦炉厂中通常能很好地监测H2S 和 O2。然而，对氨，萘和苯的测量采用传统的化学湿法只能每天测量一个样品点。最近质谱用于在线监测焦炉气体纯化厂扩大了气体组分的测量范围。研究发现在线监测能优化气体纯化过程。而且，质谱对所有气体组分的分析扩展为推导气体的燃烧特性。这点十分重要，因为气体不仅在其他过程中用作燃料，同时也用作加热焦炉本身。这些特性包括：热值，密度，比重，华比值，按化学计量组成所需的空气量。对气体的推导计算能更有效地利用燃气并且节约大量成本。表二所示为常测的焦炉中的气体组分。
Table 2: Typical composition of coke oven gas and precision obtained by PMS
Range of sample gas (mole %) concentration / Precision (mole %)H2 / 62-64 / 0.08
CH4 / 22-25 / 0.05
NH3 / 0.013-1.3 / 0.001
H2O / 2.2-2.5 / 0.01
HCN / 0.071-0.12 / 0.02
CO / 5-6 / 0.05
N2 / 1.5-2.7 / 0.05
C2H4 / 1.85 / 0.01
C2H6 / 0.85 / 0.01
O2 / 0.1-0.15 / 0.002
H2S / 0.23-0.49 / 0.001
C3H6 / 0.1 / 0.001
CO2 / 1-1.5 / 0.005
C6H6/ C7H8/ C8H10 / 0.17-0.86 / 0.001
C10H8 / 0.0007-0.025 / 0.0002
Blast Furnace 高炉
In a blast furnace, coke is used to reduce the ore (iron oxide) to iron. Large quantities of gas, ‘top gas’, are formed at the top of the blast furnace as a result of the reduction of iron ore and the combustion of injected coal by injected blast air.
在高炉中，焦炭将铁矿石（铁的氧化物）还原为铁。在还原铁的过程和由鼓风注入的煤的燃烧过程中，高炉顶部生成大量的气体。
Gas analysis is used to optimize the blast furnace process, including reducing the consumption rate of coke and controlling the temperatures inside the furnace (ref 4). Analysis of hydrogen is very important for early detection of cooling water leaks that may result in considerable damage and even explosions (ref 4). Typical composition of blast furnace gas measured by PMS is shown below in table 3.
气体分析用于优化高炉过程，包括还原过程中焦炭的消耗速度和炉内的温度控制。冷却水的泄漏会导致严重的损坏甚至爆炸，因此对氢气的分析尤为重要。图三为由过程质谱测量的高炉中的组分。
Table 3: Typical composition of blast furnace and precision obtained by PMS
Concentration (mole %) / Precision(mole %)
H2 / 4 / £0.005
CO / 24 / £0.03
N2 / 46 / £0.02
O2 / <0.01 / £0.001
Ar / <0.01 / £0.001
CO2 / 26 / £0.02
Example check gas repeatability data over a several days obtained during instrument commissioning to verify analytical performance is shown below in figure 4. The excellent repeatability of the CO and CO2 measurement by PMS should be noted.
图四为连续几天对仪器气体测量重复性测试的结果。可以看到采用过程质谱测量CO 和CO2的数据高度重复性。
Figure 4: Analytical reproducibility by PMS
Additionally the linearity of the measurement by PMS has been verified by analyzing CO and CO2 at various concentrations based on a single-point calibration. In fact the results obtained, as seen in figure 5 were within the tolerances of the certificate values of the calibration gases.
图五所示为采用过程质谱基于单点校正在不同浓度测量CO 和 CO2的线性度的测试结果。从图五可以看出，测量值完全在校正气体的真实值的公差范围内。
Figure 5: Analytical linearity by PMS
As well as measuring the gas component concentrations, the following derived values are utilized. Where the gas species given in brackets refers to the molar % concentration:-
在测量气体组分浓度的同时，下面的推导值也被采用。括号内的气体采用摩尔浓度：
Gas Efficiency, % = 100 x [CO2]/ ([CO2] + [CO])
出气率
Calorific Value (CV), MJm-3 = 0.1078 x [H2] + 0.1263 x [CO]
热值
Specific Gravity (SG) 比重 = 0.0006958 x [H2] + 0.009663 x [CO] + 0.009669 x [N2] + 0.011044 x [O2] + 0.0138 x [Ar] + 0.015185 x [CO2]
Wobbe (Wb), MJm-3 华比值 = CV/(SG)0.5
The ‘gas efficiency’ value is an important parameter used to optimise operation of the furnace. Some PMS users also take measurements from a probe inserted into the blast furnace stack itself (a ‘below burden’ probe).
出气率是非常重要的参数用来优化高炉操作。一些质谱用户也将探针插入高炉烟囱来测量。
It has been estimated that the reduction in coke rate after implementation of PMS gave a pay-back of less than 3 months.
通过实践证明，对过程优化而减少的焦炭用量所产生的能源节约，其经济价值只需用3个月的时间就能抵偿一台质谱仪的价格。
BOF 氧气顶吹转炉炼钢
In a steel plant the basic processes for conversion of iron (from blast furnace) and scrap into steel are removal of sulphur and reduction in the carbon content to the required level.
炼钢的基本过程是除硫，降低含碳量到所需水平的过程。
In the basic oxygen steel making process, referred to as BOS, BOF or LD, typically the carbon content is reduced from 4% to 0.05%. In this process high purity oxygen is blown through molten hot metal via a lance at super sonic speed, in a process that lasts only about 30 minutes. The oxygen reacts with carbon to produce CO and CO2; analysis of these gases is used to control operation of the lance to improve process efficiency and also to detect the process end point. The benefits are very great:- process turnaround is improved, re-blows are avoided, as is undesirable oxidation of the metal (ref 5).