This looks like it could take a longtime to start up unless you use a start up heater . You need to get to 500 C in the chemical absorber. The equipment will expand as it is heated and there may be adsorbed water that need to be vaporized and released slowly and carefully (via holds at various dry out temperatures) A small fired start up heater would make starting up a lot easier but if you want to stay away from burning fossil fuels or even the H2 you produced (even for start up) you could start up by circulating H20 between the photochemical rector and the absorber and LT thermal reactor until you get to the require operating temperatures near 500 C. Ideally you could use ammonia but a different heat transfer fluid (probably Steam/water) might make starting up easier/ Once that loop is established and all of the temperatures are where the should be you can start making product.

You could possibly inject cold water to maintain the temperature holds that are probably required to start up safely.

For an actual design you will need to develop a detailed equipment list/drawing that include startup and shutdown facilities. Normal operation look much easier since all equipment will presumably be maintained at a constant temperature and pressure.

If all you are currently concerned about is the heat and material balance during normal operation that is much easier because everything should normally be constant at design conditions and the heats of reaction are well known. I would assume 5-10% heat loss (mostly from hot insulated piping) for a design case.

You will nee to figure out how you are going to cool the 1000 C effluent (O2 and SO2) from the thermal reactor. If it was my commercial design I would produce high pressure steam to do work (pumps/compressors etc/) or generate additional electric power.

@Rick Manner

The chemical absorber operates at 120 C . I have an idea of the list of equipment (not a clear one though) from the process description below

In the photoreactor, ammonium sulfite (NH4)2SO3 and water react to produce H2 and ammonium sulfate, Hydrogen gas is separated from the aqueous ammonium sulfate (NH4)2SO4 solution by venting it from the photoreactor through a flash drum. Aqueous ammonium sulphate is pumped to a series of heat heat exchangers that preheat it before being fed into the LT reactor to release ammonia and form zinc sulfate. Hot product gases from this reaction (NH3 and H2O) are easily separated from solid zinc sulfate and allowed to expand in a turbine (TURBINE1) to generate electricity the exit stream from the turbine is sent to one of the heat exchangers to heat ammonium sulphate. while the solid product ZnSO4 is decomposed in HITEMRXN to release oxygen and form zinc oxide and sulfur dioxide. I also would the cool 1000C effluent (SO2 and O2) by generating electricity and is further cooler/ cooling tower. But I don't know how to approach the design of this process, should I work from a simplified diagram and slowly add the heaters and pumps required? Also how can one perform the material and energy balances, I lack the kinetics data and there are alot of recycle material streams I am only given the production rate

You need to figure out how the heating and cooling work you probably need some high temperature heat exchanger or a quench for the HT thermal reactor (870-1000 C) effluent. It seems to me that you have a lot of high level heat that should probably be used to produce High pressure steam that produces electricity and.or runs whatever pumps and compressors you need

The aspen plus does not have a photocatalytic reactor, now if you have the reactions that occur you could use a stoichiometric reactor for each chemical reaction since each one has a different temperature, in the aspen plus it corresponds to the Rstoic module, if you use this reactor you Conversion or extension of each chemical reaction would be required. In the case of the absorber tower the aspen plus if it has a module for this, in the absorption stage you must use the ELECTNRTL properties package, this is a properties package that uses electrolytes, in the aspen plus when you define the components you are going to elect wizard and define the electrolytes and absorption reactions involved in your absorption process. In the case of exchangers and pumps if there are modules in the aspen plus, in the case of exchangers if you have the inlet and outlet temperature, he calculates the heat transfer area, but as you tell me you do not have the specifications of the temperatures of exits, I recommend that you carry out a bibliographic search if there is any work similar to this or a similar plant where they have simulated in aspen plus, if you have more information and more details you tell me, this is the only thing I can tell you in Depending on the information you give me, I am knowledgeable about the aspen plus program, but I have no experience in its subject, I hope it helps

Arael Alfonso Cardero Rick Manner

" Hydrogen is produced at a rate of 11,199 kg/hr based on 12 hr/day operation in the PHOTOCAT reactor. In the photoreactor, ammonium sulfite (NH4)2SO3 and water react to produce H2 and ammonium sulfate in the presence of a visible light activated photocatalyst. Hydrogen gas is separated from the aqueous ammonium sulfate (NH4)2SO4 solution by venting it from the photoreactor (represented by the flash separation tank (FL-H2)). Aqueous ammonium sulfate solution is then pumped through a series of heat exchangers that preheat the brine before it is fed into the first solar thermolytic reactor LOTEMRXN to release ammonia and form zinc sulfate. Hot product gases from this reaction (NH3 and H2O) are easily separated from solid zinc sulfate and allowed to expand in a turbine (TURBINE1) to generate electricity. The exit stream from TURBINE1 is sent to the heat exchanger HX-9 while the solid product ZnSO4 is decomposed in HITEMRXN to release oxygen and form zinc oxide and sulfur dioxide. Hot gases SO2 and O2 enter heat exchanger HX-2 and are cooled by the ammonium sulfate stream entering LOTEMRXN, SO2/O2 and NH3/H2O streams are reacted in SFIT-GEN producing aqueous ammonium sulfite and a moist gaseous oxygen stream. The aqueous products are collected in an above-ground tank (STORAGE) and allowed to cool down during the night - to be used later as a feedstock for replenishing the photocatalytic reactor. The oxygen stream O2-EX is further cooled in a heat exchanger HX-1 and cooling tower (TOWER). The moist oxygen leaving the cooling tower enters into a flash evaporator (FL-O2) which recovers condensed water and releases the oxygen into the ambient air. Water H2ORECY collected in FL-O2 is combined with the makeup water and ammonia stream exiting HX-9 and sent to TOWER2 where it is condensed and fed into the sulfite synthesis reactor SFIT-GEN."

"LOTEMRXN, HITEMRXN and SFIT-GEN have been simulated using Rgibbs model. In the present flow sheet, PHOTOCAT is simulated using a stoichiometric reactor model. A ratio of about 10 moles of H2O per mole of (NH4)2SO3 has been assumed in the simulation".

I carried out a bibliographic search and I found out the process flow sheet employed in ASPEN as above but its not complete. From this point when it comes to defining design specs, I don't know how many will be required to ensure model convergence. I thought about a few design specs in which I can define such as the conversion of the photocatalytic (stoichiometric reactor), the recovered water from the moist oxygen stream entering the flash separator, the makeup water added to the water condensed, I also thought to myself that the electricity generated could drive the pumps added or be employed in producing high pressure steam to heat the ammonium sulfate entering the low temperature reactor. I am new to using ASPEN plus, in addition to the problem of me lacking insufficient info.

I believe this process of H2 production from H2O taking help of NH3 -SO2 -ZnO route is successfully tested in Lab Scale. The reaction kinetic and yield of each reaction is very important to take decision to proceed to the mini pilot scale plant.

Hysis simulation using Aspen tech would be useful only after establishing above aspects. Various unconventional Reactor model may not be available in Hysis environment.

The aspen Hysys or aspen plus simulator has the stoichiometric reactor models: Rstoic in aspen plus and Conversion in hysys, equilibrium, performance: Ryield, The reactors that model the kinetic are the piston flow: Rplug flow and continuous stirred tank reactor: RCSTR, I recommend that you model the kinetic reactions in the Ryield and the kinetic reactions in an RCSTR, the union of these reactors, or modules will form the reactor you want. Sometimes in the simulation of processes a module does not correspond to a team so you must know what happens in detail in your process and model it separately, in this case you integrate modules to form a team.

I used the RGibbs reactor to simulate the low temperature and high temperature reactor because the kinetics is unknown (implies also, that the product distribution is unknown)

I defined the components involved in the process

ZnO, ZnSO4, (NH4)2SO4 as solid conventional components

For electrolyte solutions I used electrolyte wizard to generate the ionic species NH4+, SO3-- and SO4--

Also I added the thermodynamic properties, standard heat of formation and gibbs of formation for the following components ammonium sulfate, zinc oxide and zinc sulfate.

I am facing two issues

the product from the photocatalytic reaction is present as NH4+ SO4+ and SO3- ions at 65 degrees celsius and the reaction in the low temperature reactor involves ammonium sulphate in solid form at 300 degrees Celsius.

I thought to myself that the ions after heating did not precipiate because I removed NH4SO4(s)-->ZnSO4(s)+NH3+H2

No reaction took place, Stream in=stream out

With regard to the first, do not enter the dissociation reaction, in the component window you go to Elec Wizard, and select the electrolytes you want, and the aspen based on those creates the equilibrium reactions with all its equilibrium constants. The second thing you tell me does not simulate the reaction using the Rgibbs, you must put CISOLID in the reactor, you mark it, it is an option of the module, if it does not calculate anything, then do not use an Rgibbs reactor, use a stoichiometric reactor, it is say a Rstoic, where you put the reaction, set the conversion or several the conversion of the reaction NH4SO4 (s) + ZnO (s) ---> ZnSO4 (s) + NH3 + H2 until you meet any design specification or any other parameter, or look for a reference for the conversion interval of this reaction