Steam Installation for CD 3002

Transcription

1 Steam Installation for CD 3002 Your eye in hell Siemens Distributor

2 Siemens Laser Analytics Febr 2001 CD 3002 Steam installation manual Document number: CID Rev. 1B

3 LDS 3000 Steam installation Content Content 1. Steam purging of CD General Installation Installation example Cost Flow calculations Check point list for customer 5 Siemens Distributor I

4 Content LDS 3000 Steam installation II

5 LDS 3000 Steam installation Steam purging of CD Steam purging of CD General Using steam when purging in front of the lenses into the measuring volume has some advantages. The most obvious one is when oxygen is measured. When air is used for purging, large measurement errors will appear. This is of course a result of the fact that regular air contains ~20% oxygen. Other applications for steam purging might be when heat is required to prevent condensation of salts on the optical surfaces. If steam is available, this is the preferred solution because it is cheaper and subject to less maintenance compared to heated instrument air. 1.2 Installation When steam is used there are a couple of important issues to consider. 1. The steam must be kept overheated at all times and positions to prevent condensation in the tubes or on the optical surfaces. The curve below shows four regions in the pressure/temperature diagram for steam. The steam installation should be designed so that the operating point just before the sensor connection at all times falls inside the green region. In the border between the orange and the blue region the steam is saturated and condensation will most certainly occur when the steam is passing the steel filter due to a power loss of roughly 50 W (the power needed to keep the sensor at elevated temperature). In the top red region there is a risk of destroying the gaskets in the sensor. The margin illustrated in the figure should be such that changes in ambient temperature, changes in the power loss in the steel filter, etc does not move the steam parameters to the saturation line when passing the steel filter in the sensor. Steam temperature [ C] Region with risk of overheating the sensor Safe region (required steam quality just before the sensor connection) Minimum in safe region Temperature margin of 20 C Saturation line Steam flow Region with moist steam Absolute pressure [bar] Saturated pressure region. Siemens Distributor Steam flow [l/min on low pressure side] (temperature = minimum in safe region) 1

6 Steam purging of CD 3002 LDS 3000 Steam installation 2. The C v through the sintered steel filter is 0.39 and the flow through this filter will be 300 std ltr/min if the inlet pressure is 4 bars and the temperature is 165 C. This flow is adequate for most applications but when necessary, the pressure can be increased to prevent dust from building up in the sensor air buffer tube. The flow is proportional to the inlet pressure according to the figure above. Formula for flow calculations will be found in the end of this document. 3. The steam system must be installed and certified by authorized personnel. 4. All exposed hot surfaces must be protected and properly labeled. If the steam quality turns out to be too poor the steam tubing must be isolated or the steam must be heated. Do not isolate the sensor since this may damage the electronics in the receiver due to overheating. A cold start of the steam system requires a tapping valve just before the sensor to drain the system from water. Note! Installation of tubing The recomended method when steam is connected to CD 3002 is to use rigid steel tubing. One important consideration is that the sensor must be able to move slightly when it is aligned. Therefore the last ~1 meter of the tubing should be steel tubing with 6 mm outer diameter free hanging and with an L-shape. Se the figure below. 6 mm o.d. Approximately 1 meter Steam tubing for CD

7 LDS 3000 Steam installation Steam purging of CD Installation example The following example is from our steam installation at Renova in Gothenburg:. Steel filter C v = 0,39 Sensor Needle valve flow = ltr/min appr. 20 m Stainless steel 6/4 (DN4) mm tube (~last meter) Steam temperature and pressure on high pressure side (the point just before the steel filter): 183 C / 7 bar Incinerator fire place temp = C p = -20 mbar Isolation Stainless steel 12/10 (DN10) mm tube appr. 20 m Sensor Needle valve flow = ltr/min Closing valve Steam box 40 bar 400 C Set-up example for Renova Municipal Waste Incinerator in Göteborg, Sweden. Siemens Distributor 3

8 Steam purging of CD 3002 LDS 3000 Steam installation 1.4 Cost The cost depend strongly on the plant and the figures given below can only serve as a basis for a rough estimate. Price of steam at Renova in Göteborg price/mw: 125 SEK (Heating: 200 SEK/MW, Electricity: 125 SEK/MW) price/ton: 98 SEK (At 40 bar and 400 C) flow: 300 NL/min price/year: 7000 SEK To complete the picture it should be mentioned that the energy in the steam that is put back in the system will be significant portion of what is taken and the price above will most of the time be reduced accordingly. In some plants a large portion of the total vaporization energy from the moisture content in the flue gas is recovered in a flue gas condenser producing district heating water by means of a heat pump. As a comparison the price for instrument air is about 0.1 SEK/m 3 ( SEK/m 3 ) which corresponds to appr SEK/year at a consumption of 200 ltr/min.. Powering two 0.5 kw electrical fan engines will cost SEK/year with the present price of electricity in Sweden (0.4 SEK/kWh). This will give a much higher air flow (~5-10 times) but on the other hand electrical engines suffer from shorter times between maintenance. 1.5 Flow calculations Gas flow calculations are slightly complex because gases are compressible fluids whose density changes with pressure. In addition, when outlet pressure is less than one half of the inlet pressure, the gas reaches sonic velocity in the valve. This is known as choked flow, because a further decrease in outlet pressure does not increase the flow. In this application we are dealing with choked flow. The following equation can be used to calculate the flow under these circumstances: q = 3271 C v p T 1 G g where q = flow rate on low pressure side [Nltr/min.] C v = flow coefficient (0.39 for our standard sensor) p 1 = inlet absolute pressure [bar] G g = gas specific gravity (air = 1.0, steam = 0.64) T 1 = absolute upstream temperature [K] The flow (q) of steam at p 1 = 4 bar and T 1 = 165 C through the steel filter would then be ~300 ltr/min, se figure on page 1. 4

9 LDS 3000 Steam installation Steam purging of CD Check point list for customer The below table can serve as an aid for the customer when designing the steam system. Fill out the table and calculate temperatures and pressures. Discuss the table with Siemens Laser Analytics AB. Parameter Value Unit Comment Steam box Pressurebar bar Temperature C Tubing 1 Diameter (O/I) Length mm m Isolation? Temperature loss at flow C Tubing 2 Diameter (O/I) Length mm m Isolation? Temperature loss at flow C Tubing 3 Diameter (O/I) Length mm m Isolation? Temperature loss at flow C Needle valve Pressure after valve bar In point just before steel filter in sensor Pressure bar Temperature C Flow after steel filter in sensor (from diagram on page 1) ltr/min Siemens Distributor 5

10 Steam purging of CD 3002 LDS 3000 Steam installation 6