Medium-pressure steam

There are two esdsting steam mains. These are high-pressure steam at 41 bar superheated to 270°C and medium-pressure steam at 10 bar saturated at 180°C. Boiler feedwater is available at 80°C and cooling water at 25°C to be returned at 30°C. 

Fig. 51eft. Schematic flow diagram of an ethylene plant using naphtha feedstock. CW = cooling water QW = quench water QO = quench oil LPS = low pressure steam MPS = medium pressure steam SPS = super high pressure steam C3R = propylene refrigerant and...

Cooling water is available with a return temperature of 30°C and a cost of 4.5 kW 1-y 1. Low-pressure steam is available at a temperature of 140°C and a cost of 90kW 1-y 1. Medium-pressure steam is available at a temperature of 200°C and a cost of 135 kW 1-y 1.The minimum temperature difference allowed is 10°C. 

The case in Figure 9 shows a heat recovery system of a reactor. The not recommended case on the left shows the feed to an exothermic reactor being heated by the product. In this case the temperature rise in the reactor may lead to the temperature rise in feed. The recommended case on right is safer since the connection is broken because the heat transfer is done by generating and using medium pressure steam. 

The feed stream containing H2S is incinerated with air to oxidize all sulfur compounds to SO2. The heat of combustion is partially recovered by raiding medium-pressure steam (400-600 psig) in a waste heat boiler. The gas is washed and demisted, then dried with concentrated H2S0i. The gas is then compressed, preheated, and enters a fixed-bed catalytic reactor. In the reactor SO2 is converted to S0a ... 

Ninian Stabilization, Cold Ninian unstahilized crude at 26 bar gauge 377 lbfisq in is healed in three stages first by exchange of heat with hot stabilized crude second, with steam condensate, and third, with medium-pressure steam. The hot, unstabdiz.cd crude then enters... 

The single-pressure process is also a higher net exporter of medium-pressure steam and has a lower utility requirement, and is therefore selected as the preferred option. 

The major process units include an air compressor to provide feed air to the process, and an ammonia vaporizer and superheater for pretreatment of the feed ammonia. A reactor vessel with a fixed platinum/rhodium catalyst bed quickly oxidizes the ammonia at reaction temperatures approaching 950°C. The reaction yield is 95%. A heat exchanger train immediately following the reactor is used to recover reaction heat. Reaction heat is recovered for both gas expansion (to provide shaft power for the air compressors) and for production of medium-pressure steam (at 380°C and 4000 kPa). The high-level energy available in the process is shared approximately equally between gas expansion and steam production. About 40% of all steam production is delegated to in- house process requirements, leaving about 3200 kg/hour available for export. 

Medium-pressure steam is produced in this process to provide some plant heating/energy requirements. An economic advantage is the income derived from the export of excess steam. The steam specification corresponds to requirements for in-house application at the steam turbine, and also in response to the needs of the adjacent ammonia plant. The final steam specification is a superheated medium-pressure product at 380°C and 4000 kPa. 

The steam production section comprising the steam superheater and waste-heat boiler is designed to lower the reaction-gas temperature from 645°C to 280°C (further oxidation in these vessels will also continue to produce reaction heat). Steam of sufficient quality is to be produced for export to the adjacent ammonia and ammonium nitrate plants. Medium-pressure steam (at 380°C and 4000 kPa) is preferred. 

In a typical 80,000 tons/year plant, capital costs were about 220 per metric ton in 1974. To produce 1000 kg of polymer, 1030 kg of monomer is needed, together with 1 kg of hydrogen and 25 kg of diluent. Catalyst and miscellaneous chemicals cost about 4 per 1000 kg of polyethylene pellets produced. For production, 300 kg of medium-pressure steam, 800 kg of low-pressure steam, 530 kWh of electrical energy, 200 m3 of water, 30 m3 of nitrogen, and 600 m3 of air are also required. To polymerize propylene in suspension, the same technology can be used. Catalysts now available [based on TiCl3 (see Table II)] make it unnecessary to separate isotactic from atactic materials. 

The boiling temperature of the bottoms product increases as the column pressure increases. Typically, medium-pressure steam, which has a temperature of 200°C, is used in the reboiler. 

High heat utilization is obtained by intensive heat exchange of the circulating solvent. Necessary additional heat is supplied by medium-pressure steam at 12-14 bar. 

Description The gas feedstock is compressed (if required), desulfurized (1) and process steam is added. Process steam used is a combination of steam from the process condensate stripper and superheated medium pressure steam from the header. The mixture of natural gas and steam is preheated, prereformed (2) and sent to the tubular reformer (3). The prereformer uses waste heat from the flue-gas section of the tubular reformer for the reforming reaction, thus reducing the total load on the tubular reformer. Due to high outlet temperature, exit gas from the tubular reformer has a low concentration of methane, which is an inert in the synthesis. The synthesis gas obtainable with this technology typically contains surplus hydrogen, which will be used as fuel in the reformer furnace. If C02 is available, the synthesis gas composition can be adjusted, hereby minimizing the hydrogen surplus. Carbon dioxide can preferably be added downstream of the prereformer. 

The synthesis loop is comprised of a straight-tubed boiling water reactor, which is more efficient than adiabatic reactors. Reaction heat is removed from the reactor by generation of medium-pressure steam. This steam is used for heating in the saturator (2). Preheating the... 

In the production process of an ammonia plant, a lot of process condensate is produced everyday. Usually, this kind of process condensate contains many contaminants, such as ammonia, carbon dioxide, methanol etc, which can pollute the environment if emitted directly. However, several techniques have been developed to remove the pollutants, such as stripping with natural gas and medium pressure steam, which can be applied one at a time or together, so that the recovery condensate can be reused as boiler feed water or as water makeup for other process operating units. It is very important for the plant to design a process which can solve the problem with minimum cost. This is the work that can be solved by the synthesis of MEN. 

The process condensate data is derived from the process of a Synthetic Ammonia in which 100,000 kg -hr" of process condensate is produced. All the related stream data are shown in Table 1 and Table 2. The condensate from the process consists of four contaminants mainly, which are to be removed away before reused by the boiler. There are several possible alternative processes to be selected, one is using natural gas to remove the contaminants, other is using medium pressure steam, and still others are employing both processes (in series or in parallel). 

The detailed optimal results for each stream are shown in the Fig. 2, Table 3 and Table 4. It is showed that this process condensate reusing system need three mass exchange units, one for natural gas stripping, two for medium pressure stripping. The process condensate first is divided into two streams, dealing with the natural gas and medium pressure steam respectively, and then the effluents are united and stripped with medium pressure steam again. 

Apart from the environmental fallout (elimination of emissions of greenhouse gases) this process allows one to obtain industrially useful energy in the form of medium-pressure steam (0.16 toristeaxn per ton A)- All this occurs in the absence of fuel consumption (e.g., methane) and with a negligible use of power for the movement of process fluids. 

Although Maui gas is very low in sulphur, the incoming gas is desulphurised as a precaution against poisoning catalysts used in the process. Following desulphurisation, water, in the form of medium pressure steam, is added and the mixture passed through reformer reactor tubes which contain a nickel catalyst. The tubes are located inside the reformer furnace where the process temperature is raised to 900°C and the reaction to form synthesis gas occurs. The synthesis gas is cooled to 35°C, compressed to 100 bar, reheated and reacted at 250-300°C over a copper/zinc catalyst to form a water-methanol mixture with about 17 percent water. The methanol product is reduced in pressure and passed to the methanol-to-gasoline (MTG) plant. 

An optimized heat integration results in a very low consumption of medium-pressure steam. In contrast to competing technologies, solidification of the solvent during maintenance works will not occur due to the low solidification point of NMP. 

The bottoms of the stripper is lean solvent, which is cooled against process streams and then cooling water before being sent to the butenes absorber. The butenes stripper is reboiled using medium pressure steam. 

The compressed syngas reaches the synthesis loop where it is converted to methanol in the Casale plate-cooled converter (5), characterized by the highest conversion per pass and mechanical robustness. The heat of reaction is used to generate directly medium-pressure steam. The gas is cooled (6), and raw methanol (7) is condensed and separated, while the unreacted syngas is circulated back to the converter. 

Economics Thanks to its design, the Casale split flow loop process is highly efficient for a given capacity, process benefits include low investment due to smaller sized equipment and low medium-pressure steam consumption (22 bar, superheated) of 750 kg/metric tons and almost stoichiometric raw material consumption. 

---