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All of the above documents contain concise instructions regarding the water chemistry of the boiler feed water and boiler water of steam boilers and hot water boilers, e.g. limit values for the →electrical conductivity or the pH-value.
The aforementioned harmonised European standards can be assumed to be commonly accepted codes of practice conforming to any applicable EU directives. The stated goal of these standards is to uphold minimum requirements for a safe boiler operation.
The legal requirements of conformity with any applicable EU directives result from the implentation of those EU directives into national law. The placing onto the market of steam boilers and warm water boilers is governed by the EC directive 97/23/EC (pressure equipment directive), and has in Germany been implemented as the Product Safety Act (ProdSG). The operation and surveillance of steam boilers and warm water boilers are governed by the EC directive 2009/104/EC (minimum safety and health requirements for the use of work equipment by workers at work), which in Germany has been implemented as the Ordinance on Industrial Safety and Health (BetrSichV).
The aforementioned national codes and standards are no longer being updated. Accordingly, with ongoing technological advancement, it is questionable to which extend they can still be considered to be commonly accepted codes of practice. However, these national codes and standards are sometimes still cited in operating instructions, tender specifications, and delivery contracts, thus affecting warranty claims and contractual obligations.
The application of the aforementioned further codes and standards issued by various organisations is optional, and can for example be part of a contractual agreement. The goal in these cases is to operate a steam boiler plant or hot water boiler plant in an economically sensible manner, rather than just fullfilling basic safety requirements. For example, the VGB standard VGB-S-010-T-00 (formerly VGB guideline VGB-R 450 L) is commonly applied for steam turbine plants across Europe, especially in German-speaking countries.
In the by now obsolete German code ↑TRD 611, the boiler operating mode used to be defined as either "high TDS", "low TDS", or "no TDS", based upon the →electrical conductivity of the boiler feed water. These terms are still widely used within the field of →boiler feed water treatment. Similar distinctions are also still made in the latest harmonised European standards, however without defining any specific terms. By taking into account the latest codes and standards, the boiler operating mode can be defined as follows, based upon the →electrical conductivity of the boiler feed water:
Basically, if the make-up water is being treated by a →softening plant only, "high TDS" operation can be assumed, while "low TDS" operation can be assumed in case of treatment by →reverse osmosis. "No TDS" operation requires demineralised water, meaning polishing of the make-up water – and possibly also of the condensate – with a →mixed bed exchanger, or with an →EDI plant either located upstream of the mixed bed exchanger, or used instead of the mixed bed exchanger.
The boiler operating mode is not chosen arbitrarily for a given application. Instead, it is determined based upon the process conditions and requirements, and possibly also the source and quality of the available raw water. For example, in case of steam boiler equipped with a superheater for process steam production, "low TDS" operating mode is often required in order to be able to operate the steam boiler plant with an economic blow-down rate.
In case of "high TDS" operation, the required boiler water blow-down rate is approximately 3% ... 10%, while it is approximately 1% ... 2% in case of "low TDS" operation, and ≤ 0.5% ... 1% in case of "no TDS" operation.
| design | – | shell boiler | water-tube, circulating | water-tube, once-through | |||||||
| operating mode | – | "high TDS" | "low TDS" | "no TDS" | "low TDS" | "no TDS" | |||||
| conditioning | – | phosphate / sulphite | AVT / phosphate | OT | AVT | OT | |||||
| operating pressure | bar | ≤ 20 | ≤ 40 | ≤ 20 | ≤ 40 | ≤ 40 | > 40 | > 40 | > 40 | > 40 | > 40 |
| MPa | ≤ 2 | ≤ 4 | ≤ 2 | ≤ 4 | ≤ 4 | > 4 | > 4 | > 4 | > 4 | > 4 | |
| direct conductivity | μS/cm | > 30 | ≤ 30 | 4.3 ... 8.6 | ≤ 30 | 4.3 ... 8.6 | 1.7 ... 4.3 | 4.3 ... 8.6 | 0.7 ... 2.8 | ||
| cation conductivity | μS/cm | – | – | – | – | < 0.2 | – | < 0.2 | < 0.1 | < 0.2 | < 0.1 |
| pH-value | – | 9.2 ... 9.5 | 9.2 ... 9.5 | 9.2 ... 9.5 | 9.2 ... 9.5 | 9.2 ... 9.5 | 9.2 ... 9.5 | 9.2 ... 9.5 | 8.5 ... 9.2 | 9.2 ... 9.5 | 8.4 ... 9.0 |
| hardness | mmol/L | < 0.01 | < 0.01 | < 0.01 | < 0.01 | – | < 0.005 | – | – | – | – |
| °dH | < 0.05 | < 0.05 | < 0.05 | < 0.05 | – | < 0.03 | – | – | – | – | |
| mg/L CaCO3 | < 1 | < 1 | < 1 | < 1 | – | < 0.5 | – | – | – | – | |
| iron | mg/L Fe | < 0.3 | < 0.1 | < 0.3 | < 0.1 | < 0.02 | < 0.02 | < 0.02 | < 0.02 | < 0.01 | < 0.01 |
| silicic acid | mg/L SiO2 | – | – | – | – | < 0.02 | – | < 0.02 | < 0.02 | < 0.02 | < 0.02 |
| oxygen | mg/L O2 | < 0.02 * | < 0.02 | < 0.02 | < 0.02 | < 0.02 | < 0.02 | < 0.02 | 0.03 ... 0.1 | < 0.1 | 0.03 ... 0.25 |
| oil, grease | mg/L | < 1.0 | < 0.5 | < 1.0 | < 0.5 | < 0.5 | < 0.5 | < 0.5 | < 0.5 | n.d. | n.d. |
| TOC | mg/L C | < 2.5 | < 2.5 | < 0.5 | < 0.5 | < 0.1 | < 0.2 | < 0.1 | < 0.1 | < 0.1 | < 0.1 |
* According to EN 12953-10, an oxygen concentration of < 0.05 mg/L is allowed in the boiler feed water of shell boilers with an operating pressure ≤ 20 bar, thus differing from the above requirements.
The above requirements are supposed for initial information only, and are neither comprehensive, nor neccessarily in conformance with the applicable codes and standards. For actual steam boiler operation, the applicable codes and standards in their latest issue, the operating instructions of the respective boiler manufacturer, and any recommendations by the notified body responsible for surveillance of the boiler system shall take precedence.
The above requirements are not valid for hot water boilers and pure steam generators.
| design | – | shell boiler | water-tube, circulating | ||||||
| operating mode | – | "high TDS" | "low TDS" | "no TDS" | "low TDS" | "no TDS" | |||
| conditioning | – | phosphate / Sulphite | AVT / phosphate | OT | |||||
| operating pressure | bar | ≤ 20 | ≤ 40 | ≤ 20 | ≤ 40 | ≤ 40 | > 40 | > 40 | > 40 |
| MPa | ≤ 2 | ≤ 4 | ≤ 2 | ≤ 4 | ≤ 4 | > 4 | > 4 | > 4 | |
| direct conductivity | μS/cm | ≤ 6000 | ≤ 3000 ... 6000 | ≤ 1500 | ≤ 1500 | < 100 | ≤ 250 ... 1500 | < 50 | – |
| cation conductivity | μS/cm | – | – | – | – | – | – | – | < 5 |
| pH-value | – | 10.5 ... 12 | 10.5 ... 11.8 | 10 ... 11 | 10 ... 11 | 9.5 ... 10.5 | 9.5 ... 10.5 | 9.4 ... 10.2 | 8.5 ... 9.2 |
| p-alkalinity | mmol/L | 1 ... 15 | 1 ... 10 | 0.1 ... 1 | 0.1 ... 1 | – | 0.1 ... 0.3 | – | – |
| mg/L CaCO3 | 50 ... 750 | 50 ... 500 | 10 ... 100 | 5 ... 50 | – | 5 ... 15 | – | – | |
| silicic acid | mg/L SiO2 | ≤ 100 ... 160 | ≤ 50 ... 130 | ≤ 80 ... 130 | ≤ 30 ... 80 | < 15 | ≤ 2 ... 30 | < 2 ... 10 | < 2 ... 10 |
| phosphate | mg/L PO4 | ≤ 20 | ≤ 15 | ≤ 10 | ≤ 10 | ≤ 10 | < 6 | < 6 | – |
| sulphite | mg/L SO3 | 6 ... 12 | 6 ... 12 | 6 ... 12 | 6 ... 12 | – | – | – | – |
The above requirements are supposed for initial information only, and are neither comprehensive, nor neccessarily in conformance with the applicable codes and standards. For actual steam boiler operation, the applicable codes and standards in their latest issue, the operating instructions of the respective boiler manufacturer, and any recommendations by the notified body responsible for surveillance of the boiler system shall take precedence.
The above requirements are not valid for hot water boilers and pure steam generators.
2018-05-05 • water treatment made in Germany • Company Information • Privacy
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