*2.9. Summary of Technical and Economical Data*

The following two Tables 1 and 2 give an overview of the technical and economical data of the different technologies. The described parameters are the basis for the technical and economical analyses of substituting a steam system with natural gas fired boilers. The two tables include more technologies than analysed in the upcoming case study. For this reason the compared technologies are marked bold in the tables.


**Table 1.** Technical data.

<sup>1</sup> = Maximum service period depending on country.


**Table 2.** Economic data and others for steam systems with 9 bar and 175 °C.

<sup>1</sup> = Small-sized: 100 m2, Large-sized: 15,000 m2; NG = Natural gas, BG = biogas BMe = Biomethane, Biomass = wood pellets or wood chips.

## **3. Methods**

This section presents the methods and concepts for analysing the steam production costs and *CO*2,*e*-emission reduction potentials via a dynamic simulation for one year. First, the different integration concepts for the technologies are described, followed by a description of dynamic simulation. The last section describes the basics of the economic analyses.

## *3.1. Steam Utility Concepts*

Since the seven different technologies have different technical restrictions in terms of availability of steam supply and start up time, different concepts of implementation have been analysed. Except the BGB and the EB, all technologies only provide base load steam which therefore requires an additional peak load boiler for the fluctuating steam demand. In addition, the MGT and FC provide electrical energy as a byproduct. This electrical energy is first used to meet the plant's electrical energy demand and only excess energy is sold at the stock market.

Figure 1 gives an overview of the set up of the reference case and first four concepts and subconcepts which are compared to the *CO*2*e*-emission reduction potentials and related economic consequences for changing the steam generation from fossil to renewable energy.

The first concept is split into two subconcepts. Subconcept 1.1 replaces the two natural gas boilers with two BGB by changing the burner of the existing boilers. Subconcept 1.2 uses biomethane instead of natural gas. In the second concept one EB replaces both natural gas boilers due to the quick reaction times of the EB a back up is not necessary. Both, subconcepts 3.1 and 3.2, integrate a BMB into an existing utility system. In subconcept 3.1 a natural gas boiler is used as a backup boiler and in 3.2 a BGB is used accordingly. The fourth concept uses a biomethane-fuelled FC for the baseload and a natural gas boiler as a backup boiler. Figure 2 shows the concepts 5, 6 and 7 in order to substitute the two natural gas boilers.

In fifth concept, the MGT is used to pre-heat the combustion air of a BGB and the produced electricity is sold to the market. The PTC and HP are integrated as baseload technologies which charge the steam accumulator. Both, PTC and HP, use a natural gas boiler for backup and peak loads.

**Figure 1.** Overview of reference case and steam utility concepts 1–4.

**Figure 2.** Overview of steam utility concepts 5–7.
