10/6/2015

Steam and hot water boilers are used in industry and public service mainly to provide steam for supplying heat and for sterilisation purposes. Due to the fact that at least demineralised water is prescribed for steam boilers to avoid calcification, water treatment is necessary in order to operate the boiler correctly. Normally this involves softening. If the untreated water contains high levels of carbonate hardness, decarbonisation or reverse osmosis with upstream softening is carried out.
The reverse osmosis technique has several advantages. No aggressive chemicals are used in practical operation. Boiler systems are automatically converted to a low-salt mode of operation. This can enable significant savings due to greater densification and less sludge. Investment in appropriate retrofit equipment may be amortised in a very short time.
In addition to calcification, damage to the boiler due to corrosion must also be prevented. For this reason, oxygen is normally removed from feed water by thermal degassing. The feed water container required for this purpose must similarly be protected against corrosion. Correction chemicals, such as phosphate or chemicals containing polymers to prevent deposits of hardness, and sulphite to bind residual oxygen, are used to protect the boiler. As well as measuring the water hardness and the correction chemicals, a range of further measurements, which are recommended either by the boiler manufacturer or by the TÜV, are necessary for operational reliability.
These measurements can be carried out regularly and automatically using modern analysis techniques. Proven and, in some cases, specified laboratory methods are reflected in the fully automatic measuring instruments. Time-consuming and error-prone manual measurements are a thing of the past. All measured values are stored in an electronic boiler house logbook. The data can be read out using established file and interface formats and transmitted to high-level control rooms. Parameters, which, according to technical regulations for steam boilers (TRD 801), have to be entered daily in the boiler house logbook, are therefore determined online. Advantages of online measurement:
• Improved operational reliability
• Improved documentation
• Improved quality of measurement
• Reduced costs
Electronic boiler house logbook
Stadtwerke Gießen AG in Hesse supplies around 190,000 users in the city and its environs with more than 400 TMWh of district heating each year. A modern combined heat and power station with heat network uses the primary energy from natural gas and biomass in an optimal and environmentally friendly manner as a result of power-heat cogeneration.
The water analysis for the five heating boilers, the feed water and the condensate return is fully automated and connected to the central process control system. 
“The central measuring station provides a transparent process image with 22 individual measurements per cycle in more than 30,000 analyses per year.”
The choice of measuring points is determined by the way in which the boilers are operated. Parameters such as water hardness, conductivity and pH-value are measured in the condensate return and in the drop before the thermal degassing unit after the chemical dosing points. Depending on the chemicals used, parameters such as sulphite, phosphate or customer-specific conditioning agents in the boiler water, as well as pH-value, m-value and p-value are measured online.
This split enables the quality of the boiler water and of the boiler feed water to be determined separately and independently of one another. The number of measuring points required depends on the number of boilers which run independently. If, as in this example, boilers 1, 2 and 3 operate as a function of the load but never at the same time, measuring points are combined (here P3). The evaluation electronics assigns the measurement correctly to the boiler which is ready to run.
The sample strands are automatically cooled at a central point and, after throttling, are fed to the online measuring station. The networked analysers are able to analyse up to 6 sample points in sequence. One analyser is configured as the master controller and automatically controls the taking of samples. A data record with 22 individual measurements is produced for each sampling cycle at adjustable time intervals and sent to the power station control room, where further decisions are made. Open software architecture also enables the user to make his own modifications.
The right online analytics for every application
Depending on the application and the size of the boiler house, we offer different sized measuring stations, which automatically determine the relevant parameters online at adjustable time intervals or event-controlled and write them to a database. An electronic boiler house logbook is available for visualisation. The project was implemented together with Wolfgang Kiebert Industrie- und Verfahrenstechnik in a leading role.